We don't generally see an overfilled system. That kind of puts the rest to bed.
a) a waste of fluid
b) messy and dangerous (if you spill it on sensitive body parts)
c) you would have to drain the overfilled system
d) a waste of time walking to the store 500 meters away to get fluid and a handpump
e) you don't get to stay dry and warm in the cockpit
a--If we need fluid, we need fluid. We don't see overfilled systems, so if we need fluid it's because we're short in one , system.
b--Bigger danger slipping while filling. Don't spill it on sensitive body parts. Same applies for a lot of other things, including the hot coffee upstairs.
c--Not a problem, because we generally don't see an overfilled system.
d--Our store is onboard, and the airplane comes with a built-in pump; it's part of the hydraulic system at the refill point in the left body gear well.
e--There's a lot to being said for staying warm and dry, but it's really neither here nor there if the airplane needs servicing.