Discussion: Book trailers

Book trailers seem to be getting more and more popular. Almost every book that comes out has some youtube video that goes along with it. 
I have to admit, I don’t see the point of these book trailers. I almost never watch them. I can see how they appeal to certain people. I guess I’m just not one of them. 
So, here’s my question to you. Do you watch book trailers? Do you think they are useful? Why/why not?