I think it allows you to see what your actors are doing when it's not you and you get to see true customer reaction so you can fix what doesn't work. I end up constantly walking through the houses, and I let them know that I am so that they are on guard consistently.
I'm a haunt junkie! I know alot of haunter prefer to SCARE people, but I love to BE scared. and this has proven valuable when checking on actors. I'll walk through with groups (or if a single person comes to walk through, i'll go with them) , I also follow behind groups (far enough back so actors don't notice me and i peek around the corner, through doors and peep holes to get the reactions and scares) but I also pop into rooms without telling the actor and i'll get a scare with them. Each of the three keeps my actors on their toes. They never know when i'll be in or how i'm gonna be coming. BUT when they see me in a group, they do their best to scare me any way they can. It's like a constant challenge for them. If they can still scare me on Halloween night, I say that's a job well done.