Now, unsupervised, that could be a problem
All night long all I hear over the radio is, "Dave what time is the screening?" Then when I actually get ready to start it I have to check every person to make sure that they work there (24-plex and I don't know the floor staff) against the payroll. It wastes my time, which I need to teardown prints (thanx to TES). 
I won't allow them to bring a guest, we have enough problems keeping the staff under control. I reserve that privilage for other managers, and for my booth staff. Gives them a little extra perk for the hard work they do. The staff hangs out in the lobby, bothering guests and making idiots of themselves, gives the theatre a bad image.
Yes, there can be problems with staff but that is easily solved by refusing to show movies for them until they learn to behave. I did stop the staff showing for a while because one or two employees chose to show up drunk/stoned. I pointed the finger at the guilty party and told the rest of the staff thay they were not having movies because of that person. Problem solved.
As I said this is done by me or my manager on a voluntary basis. No one gets paid. It is just a perk for the staff.
I have found in the past that as long as young, immature assistant (and sometimes General) managers are in charge of this nonsense, the integrity of the screenings is comprimised.
OK, I guess I'll get the ball rolling with a horror story. I was working in the booth when the staff wanted to screen a print of "G.I. Jane". All the regular shows had ended, but the managers wanted me to wait for some employees from another theatre. I told them I'd wait for a little while, and gave them a specific time that I would start it, whether their buddies had shown up or not. Well, that time came and they hadn't shown yet, and I started the movie and went downstairs to sit down. At that point, one of the assistants went back upstairs and stopped it. After the projector started and stopped a couple more times, and after some feirce arguments, I went home. Apparenty, once they finally got it going for real, they had DTS problems and had no idea how to fix it.
Beleive me, I have worse stories than that. Personally, I feel that it's not worth the arguments and bickering just so that the employees can see a movie early. Isn't it enough that they get to see it for free anyway? What difference does it make WHEN they see it?
Exactly my point.
I guess this really isn't a screening horror story but...
I was training a new projectionist and after a couple of days started letting him thread and start a few without me checking everything. Well he had a brain wrap and so I had to fix it. I had pulled out the wrapped section and wound it up onto a 2000' reel so that I could build it back onto the platter and drop it back in. I realized just before builing it back onto the platter that it was tails up so I went to rewind it.
A manager (who thought they were profescent in booth) decided I didn't know what I was doing and demanded that I give them the film so they could fix it. I started to refuse but then decided to let her take over. I left the building while she tried to fix it (I was a bit pissed off) and after about 20 more minutes the show had been cancelled, the guests sent home and the print was still not back togeather properly. After more than an hour the manager gave up and I fixed it within 10 minutes. She never tried that again. 
Moral for all managers: Why have a projectionist if you don't trust them to do their job?
They can wait until a public show to see it. The whole thing is carelessness toward the safety of the staff any way you look at it. So long as the staff gets to see the movie for free, it shouldn't matter if they have to wait 3 days for opening weekend to pass.
So what if somebody gets hurt?
He yelled, "Who keeps turning this down!?!" I told him to stop, that people were complaining about it, and that the level was fine where I'd set it. He hurled back some insult and said he wanted to show off the sound system.
People's ears were bleeding! What a moron.
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Better Projection Pays!
We almost never have trouble finding people to screen. Whoever is in charge just says, "You're in this movie... You're in that movie, etc.
We had a lot of trouble when Star Wars (rerelease) came out. There were about 20 people standing around watching me build the print(s) asking, "When are you going to be done?" I kept answering, "The longer you BUG me, the longer it's going to take!"
Well, one smartass said, "I bet you can't get it on screen in 1/2 hour." My smart assed answer was, "If I do, you have to BLOW me!" -- Well, the place cleared out in a hury. I never did have any more trouble after that!
Ever try to have a technical conversation with your sound man when YOUR ushers tell you to shush cuz dey iz watchin a moooveee!!!
And come on erika.... you can kick these kids asses!!!