Ur right, heard it from Mugen infantry, since if we add a negative poweradd, the power would decrease & occasionally at some point it will go to a negative value before getting converted into 0. ex:
Power add is -2 every tick
power = 13
each tick = 13, 11, 9, 7, 5, 3, 1, -1
since its -2, the value would at one point become -1 before becoming 0
So adding power <= 0 is more effective & triggers faster