Rod 1 said:
Overfilling is very bad for the engine. Not the environment
BB
Reminds me of a joke.
ATC: XX flight XX, turn left 10 degrees for noise abatement.
XX: Noise abatement? We're at FL300 and no one can hear us up here.
ATC: Have you ever heard the massive boom when two airplanes collide at FL300?
Anyway, back to overfilling. I'm not quite sure about dry sump engines that are properly burped, but wet sump engines that are overfilled may have the oil level higher than the bottom cylinder walls. So the pistons are banging against the oil. This may cause sloshing, foaming and whatnot, and may even cause hydraulic lock. All are pretty bad for the engine.
In addition to that, a crash because of engine failure is an environmental concern in addition to a whole slew of other concerns. When I landed at a grass field after having suffered a bird strike against the wing, the first thing that the airport manager looked at was the location of the bird strike relative to the fuel tank, to make sure there was no chance of a fuel spill.