VeryGnawty
I agree 100%
Any exercise helps the entire body. There is a trickle down effect. As long as you aren't pushing yourself, you are good to go. Personally, I find that working out all muscles equally (or at least rotating groups) to be much more usefull than focusing on one thing. If you do two hundred crunches and nothing else, you aren't really helping yourself very much.
But I'm of the opinion that exercise has very little to do with general health, or even strength. While you can increase health and strength with exercise, you can do the same thing about ten times faster simply by changing diet.