True, I bet some girls overact, but when it comes down to it, you're controlling vibrations inside her and or against her clit. You can intensify them, and control how long they last. Sure, some girls might milk it, but imagine if someone else had control of a lubed up hand sliding up and down your cock. Exactly how much clear thinking could you do, not knowing if or when it would stop, how fast or slow it was about to go, etc.?
If properly used, you can get a girl to do a LOT in the heat of the moment that she would not have done if thinking more clearly.