Before joining a group, I definitely do take the size of it into consideration. My favorite type of groups to join are the ones that are just starting off. It gives you a chance to get to know the creator of the group very well and allows you to connect with people better. When joining a large group with say, 100+ members, it already feels as if relationships have been established and you are the outsider. This is not always the case, but it's just difficult sometimes to really have a voice in a larger group. Also, in role-play, the plot can become very confusing with tons of people and tons of characters getting involved in tons of different events. It does make a very interesting sort of feel though to have a fast-paced, large role-play.