It's best to just show up though. There is a strong correlation between not showing up for lectures and failing the course. While causation may only be partial, the point is that if you always show up for lectures you're bound to put more time in the course. It's hard to diligently do everything by self study and get on the same level as you would have taking all the lectures.
Having said that, I tend to skip a lot of physics lectures. Don't really care about my grade that much in those courses.
Of course, that's a given.