Thomas Cutting at Computerworld has this wonderful quote in How to Manage by Procrastination:
There's a time for every out-of-scope project task, and the time is later.
This sort of came up in my class on Monday night. We were talking about Theory of Constraints and Critical Chain Project Management, and the issue of Parkinson's Law arose (as it does when introducing CCPM). Everyone understood the problems associated with work expanding to fill the time. You get gold plating, undocumented features (that cause more problems than they solve), feature creep, off-the-wall requests... All the stuff that this quote suggests should be done later. And Cutting even offers some thoughts on how to effectively procrastinate those tasks.