I've come across a few.
Gibson headstocks are angled back 17 degrees. If you let the guitar fall flat on its back, there's a fair chance the blow, plus the tension in the strings, will snap the neck somewhere around the E-string tuners and the nut. Breaking the neck where it joins the body happens occasionally. I've only seen it once though.
They can be repaired, but I'd not have too much confidence in the guitar.
I imagine it won't do anything to improve the sound.
So I'm very careful with my Gibsons. Fenders - you can play cricket with them.