Personally, I would make sure I got through FA with a fine-toothed comb the first time through. But after that, you should more or less know the things you are good at.
At that point, I think that you need to be careful, and weigh the benefit of a 'complete runthru' v targeting the areas where you are weak. Personally, I don't think it's worth it do a fourth run of a subject you know, when you could have done extra time on the stuff you don't.
If you know some isolated fact; it's really not worth rehashing. If you don't know a page and it will take you 6 times through to learn it, then you should do that page 6 times thru, but you probably don't need to read the whole book.
Know thyself.