Sounding like poo is only one reason clipping is bad, Overheating is another.
The way I understand it is a good sine wave looks like rolling waves. A clipped signal is flat at the tops and bottom og the waves. In subs for example the cooling comes from the movement of the sub. Since your subs aer a mirror of your signal they are staying out and in a fraction of a second longer thus overheating.
As far as amps go it gets them hot as well, but I don't know exactly how.
If I'm wrong someone like James or sometone can call me names and set us straight