With a weigh carrying ball mount, the hitch carries all the weight of the towed load.
Weight distribution uses additional mounted hardware (spring bars) to transfer load to the frame of the tow vehicle itself. In this case the hitch does not bear all the weight like the weight carrying ball mount.
According to eTrailer.com:
As long as the total loaded weight of your trailer is under 5,000
pounds and the tongue weight, vertical load the coupler exerts on the
ball, is under 500 pounds than a weight distribution system is not
necessary. However, if either of these figures is exceeded, a weight
distribution system will be needed.
Of course, follow the specific towing capacities of your vehicle. In other words, if your total loaded weight, including the trailer, 3,500 max trailer weight, 350 max tongue weight, you should use a weight distributing hitch.