From what I understand (living next to a Mormon church/mission at MSU) in order to become a member of the church (as a young adult) you have to go on mission. You also have to raise your own support for you mission.
I think it's a great idea. Making fresh out of high school kids work on the mission field makes them mature quite quickly and, imo, is the reason so many Mormons are successful. They learn a good work ethic from their parents and before going to college put it into practice individually. They don't wonder aimlessly for 3 and a half years at college not knowing what they want to do, all the while loosing that work ethic/ picking up bad habits.