The problem with punishing people over policy violations
Back in my entry on why user-hostile polices are a bad thing I said that I believed threatening to punish people was generally not an effective thing from a business perspective. I owe my readers an explanation for that, because on the surface it seems like an attractive idea.
The problem with punishing people is that practically by definition a meaningful punishment must hurt, and generally it can't hurt retroactively. However, when you hurt people and especially when you hurt people's future with you (through bad performance reviews because of policy violations, docking their future pay, and so on), the people involved may decide to react to the hurt by just quitting and finding another job.
This means that any time you are contemplating punishing someone in a meaningful way, you must ask yourself whether whatever they did is bad enough to risk losing them over it (or bad enough that you should lose them over it). Sometimes the answer will be yes that it was really really bad; sometimes the answer will be yes because they're easy to replace. But if it was not a really bad thing and if they would be disruptive to lose and a pain to replace, well, do you want to run that risk?
Obviously, the worse your punishment is the higher the chance of this happening is. In particular, if your punishment means that they'll wind up noticeably underpaid relative to their counterparts elsewhere (whether through denial of promotion, denial of performance raises, or so on) you'd better hope that they really love working for you.
(You can always hope that they'd have a hard time finding another job (or at least another job that's as attractive as yours even after you punish them) so that they don't really have a choice but sucking it up and taking it. But for high-demand professionals this is probably not very likely. And even if it's the case now you've armed a ticking time bomb; I suspect that you're going to lose them as soon as they can go.)
(This is separate from the additional problems of punishing people at universities, where I was more focused on removal of computer or network access than a larger view of punishments in general.)