Every once in a while at home, I play a game with an extra ball or 2 on playfield just for fun. I had previously shown a couple novice friends how the mechanics worked and how interesting it was that it was set up that way. They played a few "normal" games with me, but weren't exactly EM kind of people so I let them load a couple extra balls on just to spark interest and they had fun, respected game, no prob....
Later on, there is one of their girlfriends who decides she likes the whole multiball idea and I didn't think much of it....until I walk by and realize she is smashing the $#!@ out of the rod on my already worn ball lift trying to get all 5 up while playing. I mean she was beating the piss out of the front of my machine!! I was so frustrated because I know it wasn't on purpose, but after that....I don't like it. I may gently do it on occasion to my own machine, but would never do it to someone elses.
Long story, sorry. Just shows the mixed bag it can cause kind of like people already mentioned.