It indicates the QB's target

Instead of a QB throwing the ball out in front of the receiver so he can continue running up the sideline and catching the ball in stride, the QB's target is the "back shoulder" (or the back of the WR's helmet, depending on how you want to teach it). The pass is purposefully thrown behind the WR so the WR has to stop and adjust to the throw, which is easier for the WR to do than the DB. Hence, the advantage of the route.

I think the OP is using "back hip" to refer to a similar play where the ball is thrown lower, so the WR has to go to the ground to catch it. This is typically used near the end zone; think of it as a "back hip" throw thrown to the front pylon. It takes advantage of the DB overplaying the fade to the back corner pylon.

Yes, it does make a difference (though admittedly, the back hip is more of a goalline route). At least it does for good, accurate QBs.