Also by forcing managers to drag employees through a pip process, you: (a) reduce risk of wrongful termination suits. (b) increase likelihood that an abusive manager is discovered.

I'm sure lots bad managers get away with bad stuff, even when a pip process is in place.

But every bit of documentation produced by a pip could certainly backfire on a bad manager.

Again obviously, not all bad managers will be stopped, not will all bad employees :)