Dallin H. Oaks said on the matter of callings:
We have a great tradition of unselfish service in The Church of Jesus Christ of Latter-day Saints... This is the way men and women prepare for the ultimate blessing of eternal life.
Still, there is room for improvement in the commitment of some. When I ask stake presidents for suggestions on subjects I should treat at stake conferences, I often hear about members who refuse Church callings or accept callings and fail to fulfill their responsibilities. Some are not committed and faithful. It has always been so. But this is not without consequence... My brothers and sisters, if you are delinquent in commitment, please consider who it is you are refusing or neglecting to serve when you decline a calling or when you accept, promise, and fail to fulfill.
Sometimes a calling lasts for several months and other times for years. I would say the average length of time I have seen is two to four years in a calling. The expectation by an LDS leader when giving a calling is that the person will stay in the calling until the leader decides to release you at some indeterminate date.
The ward leader called the bishop or the stake leader called the stake president make the final determination after consulting with their two counselors and an organization's leader usually called a president. Sometimes a president of an organization consults with his or her two counselors but many times they don't. A member of the bishopric or the stake presidency usually extends the calling. A rare exception is for secretaries when the president of the organization can extend the calling or in the relief society or priesthood when you are called to visit other members as a visiting teacher or home teacher.
The bottom line is that in making a calling it is to be based on revelation or a gut feeling by inspiration. So the leader may or may not use any rational thought process in the calling. It is supposedly from God and the member accepts that the person receiving it is inspired in making the calling and in releasing or changing a person in a calling. Mormons like to joke that it is
Sometimes in filling a calling it is based on availability. An opening occurs and from the pool of available people the position is filled. Then you have to get clearance from the ward or stake leadership. Once as a high priest group leader I suggested ten men to be an assistant group leader and was turned down all ten times. In the end I told the leader just to pick someone and I would work with whoever was called. He called a less active member who came on the week he was in charge of priesthood meeting which I rotated every three weeks.
Only every two to five years is there a major reorganization in the groups or organizations. Then people are fully considered for all the positions. However during the remaining time in-between many times a new move-in fills a position. In making a calling a leader might consider such things as the person's family life, moral worthiness, skills sets, knowledge of the area or potential knowledge about the calling, health, financial condition, etc. Many times the leader calls a person because they just like them or feel good about them. I have issued callings mostly based on disrupting the least amount of people in an organization. I would look at the availability pool which might be a few people and say which of these men would be able to fill calling and not turn me down.
Since I move quite a bit like thirteen times in the last 25 years I have served in every organization at the ward level except Bishop or a bishop's counselor nor in the relief society which is a woman's only organization. I have served in all other callings including in the bishopric as an executive secretary and all other clerk positions (ward, financial, membership), as well as elder's quorum presidency, high priest group leader, young men's leader, Sunday School presidency and teacher (all classes every age), primary teacher and nursery leader, ward mission leader, family history coordinator, seminary and institute teacher, temple worker, ward librarian, etc. I even served at the stake level as an executive secretary for four years.
One of the best ways to understand what constitutes a calling and how they work is to read Rachel Woods LDS Church Callings at About.Com. Her basic definition is:
In the LDS Church which is a voluntary organization a calling is extended to a member to serve in various organizations which are broken down in a congregation or ward into ten groups: Bishopric (administration/leadership), priesthood, relief society, young men, young women, primary, ward mission, family history, and Sunday School. A calling may also be extended at the stake (synd/diocese) level in the same ten groups and an additional group called the High Council (men who oversee ten groups as well as the wards and priesthood groups under direction of the Stake President): Stake Presidency, High Council, Stake Relief Society Presidency, Stake Young Men's Presidency, Stake Young Women's Presidency, Stake Primary Presidency, Stake Family History Coordinator, and Stake Sunday School Presidency. To fully understand the organization of the church check out Wood's Organization of the LDS Church to understand the discussion if you are not a member of the church.
In the LDS Church a "calling" is a position or assignment in which members have been asked to serve or perform. Members are called of God to serve each other, and all callings are important. Callings are voluntary, are issued by the proper authority, and are usually for a few years.
Members of the church do not ask for callings nor are they consulted by the ward Bishop or the Stake President who consults with their two counselors and leaders of the various groups in the issuing of a calling. The expectation in the LDS Church is that a member will accept whatever calling is extended or given to a member. A calling is supposed to be by revelation.
In my church life I have never turned down a calling that has been extended to me. I only questioned a calling once when they called me to be a boy scout leader. I told the man issuing the calling did you know that I have never been a boy scout and don't even know how to put up a tent. I suggested he might want to consider that since he had numerous eagle scouts there might be a person better suited. The next week I was called to be an assistant ward librarian.
In home teaching assignments which change more often than other callings it is not unusual for the high priest group leader or elder's quorum president to discuss the two to five families and the effectiveness of the two home teachers. So from time to time new families are assigned. The expectation in the LDS Church is that you will be a home teacher from the age of fourteen until you die. LDS leaders resist not giving all priesthood holders an assignment since there are hundreds of members and only about one hundred active priesthood holders.
Recently I became ill with diabetes and high blood pressure with a respiratory infection and asked for a few months off from my assignment. The bishop was understanding and talked to my high priest group leader. Instead of agreeing the man ignored my request and only mentioned the bishop had told him about my request. No more communication ensued so I kept home teaching the one or two families I was assigned that I could get in to homes. I have another lady that is in a rest home but I don't have permission to visit her.
I have on a couple of occasions mentioned to leaders something like if you want to release me I don't have a problem. One of them said no that is alright you are doing a good job and the other one said I guess it is time to think about calling someone else. I have had a couple of other occasions where I was released when a bishop didn't like my personality. I was serving as a gospel essential class in Vernal, Utah when a less active young man came in to my class for the day. I made a quote by Joseph Smith which he questioned. I was right across from the library so I stopped my lesson and walked over and got a manual which I gave him saying he could read it himself. He reported me to the bishop. The bishop told me I was not a loving person and released me the next week. I found that interesting since I was teaching for several months one student who had some real issues and had three very active sisters who came so he wouldn't be alone. We seldom got any other new convert baptisms or returning less active people.
I feel if a person has something happen in their life that affects them physically or emotionally that they should be able to consult with their leaders in continuing in callings. In the end in the LDS Church it is the leader's decision to retain or release a person. If you are also not worthy sometimes it is necessary to clear the air. Also if you are burned out and feel you are not being effective I think leaders should know so they can consider other options.
I think ninety percent of the time people can stay in callings without anything impacting them but ten percent of the time things come up after a year or two from job problems to family problems to psychological issues that might make releasing a person necessary. I think most leaders don't always communicate well enough nor hold interviews to determine where people are in life so there are times a person needs to ask to be released.