Staff should understand the reasons why they are moving to a PIP, even embrace it and thank you for it. If this did not happen you need to take a look at your process before you delivered a PIP in the future.
Review Leadership chart "Know, Grow, empower and guide" http://www.whamond.net/leadership.html
Don't use a PIP as a "Bully" tactic o get what you want or to stamp your authority, you loose credibility with the rest of your team and will soon find yourself in a fast spiral of destruction.