If you're ever put on a PIP, get out -- it's a sign someone in the company doesn't want you there. I've never heard of a PIP working out and both the company and employee being happy -- maybe you only hear about the bad cases, but a PIP often seems to me like a cover your ass plan on the part of the company. They want to get rid of a person, but they're afraid of getting sued, so a PIP is a way to document why a pers…
Sometimes you might really like an employee, but _need_ them to improve on a few things for their employment to work. PIPs can definitely work in this circumstance.
Sometimes an employee is just incredibly toxic, and you may have reason to believe that they'll sue the company if you fire them without well-defined cause, (like the parent article here). In this case you are simply creating a paper trail to cover your ass legally. Of course the PIP is not going to "work" for the employee, they will be fired regardless as you want them gone. But the PIP may "work" for the company, by limiting liability.