I have to be really careful with what I watch on TV, mostly because I have this thing called a photographic memory. Basically, I remember a lot of what I see, which is both a blessing and a curse. It's a blessing when I need to remember where I left my keys (and it's great when comparison shopping!) but it's a massive curse when going to the movies, especially when the trailers come on. Some trailers are a bit scarier than I'd like them to be, mostly because those images stick in my head for a really long time (and quite frequently haunt my dreams). Most people love movie trailers because they get a heads up about what they're going to see. Likewise, book trailers are really helpful for students because the content may persuade them to read the book. For a lot of people, reading a book plays like a movie in their mind, and seeing trailers helps them to start those visualizations.