Treantmonk recommends that a "Switch-Hitting" ranger take the QuickDraw feat no later than 3rd level. Why?
It's only use is to allow the ranger to take a full attack. He won't get multiple attacks out of a full attack action until 6th level. So why QuickDraw at 3rd?
I would guess because you can spend a low level feat to pick it up and then save your higher level feats for things that require higher levels.
Also, it has other uses. It would let you put away your bow (move action) draw a sword(swift action) and attack (standard action). without this you would have to drop the bow (free action), then draw your sword (move action or as part of a move action if the move is over 10 feet), then attack (standard). The difference is you don't drop your bow.
In two words, rapid shot. Or two weapon fighting. Either or both of which a switch-hitter can reasonably have. And if you want to switch from rapid shot to two weapon fighting in consecutive rounds, you need Quick Draw.