My experience with PIPs is that they're essentially an advance notice that you're getting fired and a grace period while you finish up outstanding projects and

My experience with PIPs is that they're essentially an advance notice that you're getting fired and a grace period while you finish up outstanding projects and look for another job. There's a lot of flexibility with at will employers, but even for clear firings with just cause, it's often less risky to eat the cost of that grace period. Aside from the risk of (frivolous) legal costs, there are reputational and morale risks from departures that aren't adequately "managed." No one is ever walked into an office and fired on a Friday morning for performance reasons without lots of warnings, including a PIP.