All of the ones that last. If you don't handle your bad apples and your business requires generating a profit to survive, you will not prosper for long if you don't prune the bad apples (and you may not even survive, unless the business throws off such huge profits that it can afford to carry the dead weight).

It's as simple as "Please clean out your desk". Have you never seen The Apprentice? Do you believe that people never get fired?