Psychologically, it's much easier to "eat clean" when you know you will have an opportunity to indulge yourself later. Despite being somewhat controversial, the idea of a cheat day, or at least a cheat meal, is a common element in many popular nutrition plans and diets. Myself, I cheat every Saturday. The main reason I include a weekly cheat meal is not so much for the mental aspect or to settle any cravings, but rather to support a healthy metabolism.
The following video could be considered to be taking things too far... this is what I call my Epic Cheat Meal. Prepare to be amazed by my glorious creation! (Vegetarians, I suggest you avert your eyes!):