From SRAM's page:
TurnKey™This exclusive technology works a lot like the Secret Service. If you happen to hit a big rock when you have your fork locked out, TurnKey’s patented blow-off design takes the bullet for you, absorbing the unexpected hit instantly. When you think about it, it’s kind of noble. Compatible with both PushLoc and PopLoc remotes.
The main reason for suspension lock-out is to prevent wasted energy due to pedal bob and weight transfers. If you hit a big impact, you're not wasting pedaling energy. You may even want to consider riding regularly with the fork not locked out. If you're a relatively smooth pedaler you'll find that the lock-out doesn't actually do much and the suspension is nice for potholes and curbs.