Never have covered anything. I just don't go hog wild. I have spray washed engine bays for 50yrs and never had a problem. Recently power washed Passat engine bay. Sprayed Simple Green first and then power wash, focusing mostly on grimey block and hoses. That's my experience anyway.
Just be smart about what your spraying, keep the direct pressure away from pulleys, alternator, fuel filter top, and the battery top. Getting this stuff wet won't hurt them. I run the motor first to get it warm then let it run for a while after I finish then leave the hood open overnight.
Excellent question. I've been wondering this forever and always thought I'd ruin something if I washed it or would melt down plastic or rubber if I sprayed some sort of engine bay degreaser on it. Thanks for the tips everyone.