Brummie mentioned that his congregation's Elders simply wouldn't allow him to transfer to another congregation when he wanted to – and I have heard this approach too in some areas – but this is very localised, it very much depends on the local bodies of Elders.
I have known mass-evacuations of people to other congregations when there is a "difficult" Elder. I know of one congregation in London where there are around 50 publishers, but around 130ish brothers and sisters live within the territory. This is simply because the Presiding Overseer is a deceitful arrogant asshole, and one by one he has driven all the kind-hearted ones out, just leaving his own toadies and sycophants. Virtually everyone knows it, but he manages to charm the pants off the CO and the DO and always gets away with his power games.
Minimus, what you say is very familiar to me. Elders are often asked to attend other congregations by the Circuit Overseer as in some areas there simply aren't enough brothers "reaching out" and they need a helping hand. They in turn eventually move to the territory of the congregation they are assigned to. This doesn't necessarily happen just with Ministerial Training School graduates, lots of Elders and Ministerial Servants move to different areas because they are asked. An ambitious brother would always say yes to a Circuit Overseer, it's God's will isn't it? The reason I live where I do right now was because the "need was great" and my father was recommended to move here.
At the moment I can tell you that I don't actually live in the territory of the congregation myself and my family attend, but I'm very glad of this. The congregation that covers the territory I live in is very hard-line but the congregation I attend is more hands-off. As I am in the process of a fade I would simply not get away with slackening off to the extent I have if I attended that congregation, I would be hassled by the elders all the time.