Re-feed days, i.e. the controlled version of a "cheat day".When in a period of fat loss, a strategic day where you increase your calories can be extremely advantageous.
The reasons include: balancing hormones [including grehlin (the hunger hormone) and leptin (in charge of how full you feel)], reducing signs of fatigue, improved training performance, and avoiding a weight loss plateau. Not to mention the psychological benefits from taking a "de-load" from having to say "no" all the time.
Now, there are two approaches I like to take:
1) Consume a maintenance amount of calories, or eating until you are satisfied without over-eating.
2) Let the rope go a little more, whilst still making strategic decisions about the food choices you make - these may be consuming something like my protein cheesecake instead of the usual type, which tastes exactly the same, for a fraction of the calories.
Notice that neither case entails ruining all the hard work you've put in so far, where a traditional "cheat day" usually does.
It can take one day to undo one week (or more) of progress, and this is not the aim. The aim is to re-fuel your body whilst limiting the progress hindered, ready to kick on again.
In both cases, I also suggest increasing carbohydrate consumption as oppose to fat. Why? Because replenishing glycogen is going to aid future training performance, and make your muscles look "fuller" - as when losing fat your muscles may start to look "flat".