Well, there is anecdotal evidence that high voltage setups with low kv motors are a bit punchier.
Objectively, there are some small benefits (like less battery current for charging / discharging), but the main one I suppose is that it increases the length of the speed/torque curve on setups:
So with higher voltage you have a longer curve to adjust (with your gearing) back and forth to choose either higher top speed or higher startup torque.
Back on topic: there are extremely few esk8 ESCs that can do 20s on the market (at the moment, new ones are coming). So that makes this a tough sell.