Voyager is a good example for this as it was one isolated ship in a far away place without any crew transfers.

I still think that there were a lot of new people brought into it for extra roles instead of relying on a small pool of people.

I actually should have brought that up in my original post.

I can understand that, as i said in the case of Star Trek those are ships with over a 1000people on board, so it may make sense to always see new people.

Thanks again for staying with what i really asked. Colm Meaney is probably the best example for this.

Seems it was a pretty obvious question, i just read that the Screen Actors Guild has some pretty strict rules about stuff like that. Just for example who is mentioned in the credits and where etc. Maybe, what i was thinking about, only applies to movies.

I guess i did overthink this one a bit.

Thank for the answer, sheds a little more light on what i asked about. I put too much of star trek stuff into the question i guess, what i am interested in is really only the production side for this question.

Thanks, that is more in line of what i meant. They just use new extras because no one really cares. I was just wondering about it because i read about some laws that gives more rights (money, insurance, etc.) to people that are continually employed by a specific show in one role.

No i didn't, it was just something that came to mind when i thought about always seeing new persons that i never saw before.

But why is that so important instead of the question i asked, if there is some rule or law that prohibits using extras more than a few times without upping them to cast members?

Well they die mostly. I just meant the other bridge staff or staff in general, sometimes you see a person twice, mostly on the next episode then. But there are never recurring characters that are not on the main staff. (Edit: In Tng there is a nurse that is seen more often, that is actually what i mean, why are there not more of those "named" background characters.)

Like a person that is on the bridge now and then, or in the medical station. Those are always new people.