The point of Quick Sync is to offload video encoding to specialized hardware, which reduces CPU usage. A quick Google search confirms that AirParrot uses a lot of CPU, which hurts the user experience. I won't opine on whether this is worth dropping the feature (and of course an application could be designed to use Quick Sync if available and fall back to the CPU otherwise; would be nice if OS X exposed this as a public API, although I think it's not hard to get at anyway), but there certainly is an advantage.