content: I think for some movies, that have a twist in the end, it might ruin the actual idea of the movie. If you already have knowledge of what's going to happen, it will change the way you look at it, and change your experience as well. For bad movies it doesn't matter, because you'd only watch those once anyway, or you can avoid watching them if you already know the story is going to be bad. But if I suspect a movie is going to be good, when looking at who the director is, for example, or whether the cast has a good track record of choosing the right films to star in, I will not even watch a trailer. I might even interrupt watching a trailer if I decide I'm going to watch it.