My experience was not like some of the ones described...
My IOP had two therapists (sometimes one was out so there would just be one) and no more than 12 people but usually less depending on the day. Group started with check in where everyone speaks briefly (like 30 seconds to 3 minutes) about how their night and morning went. If they have something they need to get off their chest, they say they want to share which is done after all people get to check in. New people are welcomed at that time and given a chance after all other checkins to introduce themselves. People share and the group is very respectful, giving all the opportunity to share through the weeks. The therapists would occasionally ask the more share-ative people to give the more quiet people a chance which was nice. Most days someone has a turn to give their life story. They then get feedback from the group (always positive because we bond quickly).
It was very organized and respectful with pretty regular folks of all ages. I guess I got lucky!