Films are timed to start every 20 minutes or so and people don't just turn up as the film is about to start, they turn up early, they turn up late and so there is always a requirement for people to be at the doors taking the tickets. When we do have a spare moment we do screen checks on a regular basis to make sure the films are running smoothly, that people aren't talking and we also are constantly stocking the kiosks, cleaning up the endless stream of popcorn left on the foyer floor, cleaning the toilets etc.
There are also a constant stream of screens coming out, if you've ever seen the mess left behind after 400+ people have left their food and drink all over the floor you'll know it's not something that can be cleaned in a minute. Often it will take 4/5 people 15 minutes to sweep/mop/pick up the crap left behind and inevertibly once one screen is cleaned, another will be coming out within minutes.
Of course I haven't included box office responsibilities of which there are many.
The job is not rocket science, far from it, but it can be hard work and there is always something that neeRAB doing.