I have often wondered about the same thing as to my mind a homing switch should be in the middle of the travel and limit switches at the extremities. If a homing switch is in the middle then its construction will dictate how accurate the position will be depending which direction the position is reached from(if you get my drift! - no pun intended)
So far Ihavent fitted switches to my mill as I dont see how they are going to be that useful!

Peter