There was one time I remember reading the solutions being helpful at all, it was in precalculus (don't remember the book) and the book didn't have a separate solutions manual, instead every exercise was given with a purpose (no raw drill) and the solutions page in the back wasn't just what the right answer was, but what you should have learned and noticed in working the problem. Each page had the general admonision at the top "If you found the answer but not the reason, work it again."