I wouldn’t doubt companies would use it any place it’s not enforceable, and at least attempt to collect.

I’m not sure the nuances of it, other than having talked to a couple of people who were in that situation, talked to an attorney, and ended up paying. I would suspect having a valid reason like sexual harassment wouldn’t affect if it’s enforceable per se, but give you a lot of leverage to convince a company it isn’t worth pressing the issue.