It literally shows iterations per second per millijoule and the <10mw delta between 300/691I dont see how a benchmark utility can quantify the battery life saved by allowing 300mhz minimum. It is clearly not for performance. Our devices have more than enough performance, but many people are wanting to improve battery life. Perhaps it doesnt help, I cant say if it does or not, but the option is nice to have.
Just because you "don't see how" doesn't mean it's wrong, and you still have the option, just set the minimum CPU to 300 if you're the type of user who prefers a poor experience with considerably more lag for the extra probably 20 minutes per charge cycle of standby you'll get between screen on and deep sleep