What with the number of Apps and Scripts we're running these days, we have to be careful not to overwhelm the mTurk system. Doing so can result in warnings, or even a ban. Our Hit Stop's professional advice is to keep your Page Request Rate at or above 0.8 seconds. If you drop below this rate, please be advised that you do so at your own risk.
If you aren't using a 4th App, Enter 0 in the Additional App's Rate Box.