Depends on the aircraft and engine. Some (like my little Rotax 912ULS) has a peak power at which I can only operate at for 1 minute during takeoff. I typically cruise around 70% peak.

I believe in Helicopters you're often running at 90%+ max rated power, but on an engine that's derated from its true maximum power.

Generally speaking on combustion (piston) engines the max torque (and efficiency) is at revs between 2/3 and 3/4, sometime 4/5 of power peak revs, and in "static" applications (i.e. when you don't have an accelerator that you use continuously) such as aviation but also power generators, hydraulic loaders and excavators, etc. they normally are operated (continuously) at those levels range (around max torque).

I can’t speak to helicopters, but light aircraft engines tend to run at 80% of peak; peak is only used for takeoff and go around, to my knowledge. (Not a pilot)