Most receivers have two limits, like mine:
So the receiver may fail over its rating. Handling is often affected at or below the receiver limit as well. Adding weight behind the rear axle acts as as level with the rear axle being a fulcrum. This can overload the rear axle and reduce front axle weight. Lower weight on the wheels that turn becomes less stable at some point.
IMO for half ton pickups 400-500 pounds is the point at which WDH should be used, a bit lower than what the receivers on them are rated and my casual observation of owners using them.
Take a look at
this thread.