When I was auditing a Social Psychology course on the university channel several years ago, the professor made a very interesting statement about high control groups and the size of those groups. Apparently a group made up of 50 - 75 members was optimal for keeping the group in check. It makes it difficult for a dissenting splinter group to form, because there are less people to assume leadership roles. It is easier to gather information on individuals when you have half a dozen people in Elder type roles and another half a dozen in Ministerial Servant type roles, mostly all responsible for smaller group (book study and field service arrangement) situations.
What you'll often see among JWs is that when a couple of neighbouring congregations are all approaching the 100 publisher mark, there will be a reorganization of the congregation territory and the congregations will split, usually two congregations into three, or three into four
100 + 100 = 200 200 ÷ 3 = 66.6
100 + 100 + 100 = 300 300 ÷ 4 = 75
In this situation it also artificially creates a fairly fast turn-over rate, so that people do not develop close or very deep friendships, considering that there is a pretty constant state of flux. On a psychological level as well, the members come to believe that the growth rate is "phenomenal", because it seems like new congregations are springing up all the time, when in fact there is merely redistribution of the congregation territory.
Seeing it happening at the same time in the congregation that we were assigned to really caused one of those moments of clarity for me....