The permanent-press cycle is usually best for synthetic fibers and for wrinkle-resistant cottons while using regular (vigorous) agitation for a shorter period of time. This reduces wear and tear and pilling. It also provides a cool-down rinse, a cold final rinse, and a slower spin speed.
--Summary from Home Comforts, Cheryl Mendelson
I've always wondered what "permanent press" actually means. Now I know. Sort of. Actually, I might just keep setting it to "regular."