I know what you guys mean with books and movies. I really liked the DaVinci Code movie, especially since I read the book two and a half years ago so a lot of stuff was still surprising to me since I forgot half the book haha. But I'm really nervous to see The Devil Wears Prada because it's one of my favorite books and I don't like who they cast to play the roles. They even changed one of the characters names for no apparent reason.
But I think in the case of Senseless, it will help in watching just because you will already know what will happen to him. But if you don't want to be spoiled then definitely don't, because what I saw of the trailer seems pretty much exact to the book. It's such a short book they probably didn't cut much out either.