I've been trying to build up my muscle strength as part of my exercise regime. I'm not really interested in body building, but I've heard that muscle tissue burns something like three times the amount of calories as fat, so it seems like a good idea to have some!
And in fact, I've found it just makes everything easier. I think mostly because of the crunches and things I've been doing. I've noticed a huge difference in my looks and my general fitness since I've started.