Quote Originally Posted by MDHillSlug View Post
My swim coach had me doing free and back. I never asked why back when she knew I was training for triathlon. I think it may have something to do with exercising the opposite groups of muscles.
IME, you a better workout by swapping strokes. Less risk of a repetitive motion injury, and more muscles get worked. Also, working on form on a stroke that you'll "never use" tends to pay off. You get a better feel for how your body moves through the water under a variety of circumstances. No big deal if you're only ever in a pool, but a very big deal in open water.

I actually wish more instructors taught things like somersaults and other basic underwater gymnastics. Good way to get a "this end up" map into your brain.