And you don't even need to physically go back there to fold them down - there's a button for that!In my previous car you had to physically remove the headrests to obtain this same benefit, and then remember to put them back in if you're about to pick up someone who'll be riding in the rear. This is much more convenient and safer. I recommend folding them down if you don't need them up all the time.
EDIT: but you DO have to go back there to fold them up
EDIT2: I think someone here called this the "Guillotine" button - for passengers you don't like!