I recently heard a client say, " I have never seen an employee stick around after having been through a performance improvement process."
The challenge in many organizations is that they view discipline the wrong way. The process is filled with warnings, threats, and ultimatums, and as a result good people leave bad managers.
On the other hand, when discipline is done correctly, it can be a process that helps an employee and team be successful.
It's really about building commitment instead of compliance.