If you're using gps to track running and such, you aren't running 24 hours a day, so you can save battery by turning it on and off. I think that's a great feature. But it would have been nice to say 'GPS' time, like phones describe 'talk-time'.
I run and cycle. I and many people I know do cycle ~ 12 hours in a day, while training. Right now the choice among road bikers I know, is the Garmin 810 which lasts that long with continuous use.