There are really two questions here. To answer the first, there are several conceptual advantages that a dynamic balance arm has over a static balance arm. Tracking force is always exerted at a right angle to the record, even if the turntable is not level because that force is exerted by the notorious spring instead of gravity. When tracking warps, the spring opposes the momentum that the arm would have on both the upward motion that would diminish tracking force and on the downward motion that would increase it.
To answer the second question, practically applied, in the Rega arms, there are those that feel that the complication of the spring adds a resonant mechanism right at the bearings. They believe that these added resonances more than just counteract any benefits of dynamic balance and are deleterious to the overall sound. They prefer the RB-250. Some, like the gentlman above, believe that static balance just sounds better and set-up the dynamic balance arms to be static balance. My personal experience is that dynamic balance is superior in the Rega arms and the three gram setup did not yeild any sonic advantage in my system. Nor did turning the spring to "0" and applieing all of the force with the counterweight. My position is certainly not the popular one and your mileage may vary. Cartridges are Denon 103D, Grado Platinum and Rega Elys.