A clean break allows you to cut all loose ends. No lingering uncertainties, no hidden agendas, no unvoiced grievances. You said it all, and now you are leaving. See RightToLeave for more about "leaving."
The problem with this approach is that this does not necessarily prevent OldProblems from resurfacing later on. A clean break might hurt other parties unnecessarily; often not everything that can be said needs to be said. The difficulty lies in finding the right balance between OpenProcess and OpeningOldWounds?.
When you are trying to fade away, the main concern is to leave without offering FlameBait. This is most useful when continued activity seems to cause offense, but a CleanBreak would undermine your long-term goals. Perhaps you are just trying to let some grass grow over the issues, hoping that ForgiveAndForget will allow you to resume your relationship at a later date. Be careful to not retreat behind a WallOfSilence, however.
DiminishingReplies is an example.