Being somewhat familiar with the music before I see the film increases my enjoyment of the movie substantially. It's interesting comparing people's reactions to TFA music initially vs. after a few times through the soundtrack or movie. I remember being disappointed that some of the first reviewers for TFA weren't overly impressed by the score. I ended up loving the music and am eagerly anticipating the last jedi soundtrack. Fully expect to hear some more Jedi Steps, maybe a new Rey/Luke theme, etc. There might be some minor spoilers that us music nerds would pick up on by listening to the soundtrack early - ie, if we hear Yoda's theme in the middle somewhere and realize we're going to get Yoda Force Ghost somewhere- but it won't be anything that would truly spoil the movie.