In some organizations, you might have three levels of trips. First is a beginner trip. There will be a leader and perhaps some co-leaders to offer assistance to the typical idiot mistakes of the beginners. Possibly they can even loan gear to a beginner. There are always some problems on beginner trips. Then there are intermediate trips, and there will be a leader. However, intermediate travelers are expected to be somewhat experienced, and they know their own limits, and they don't normally have any severe problems. Nevertheless, somebody should have a first aid kit, etc. Then there are advanced trips. Normally there is a leader, but often that is more the role of organizer, because the advanced participants know what they are doing anyway, so the leader/organizer isn't trying to herd cats or something. There are few services expected of a leader on an advanced trip. Advanced participants are normally pretty self-sufficient, although arrangements for gear sharing happen. You just have to be clear about the level of the trip, and then participant expectations will go out from there.