A planned release valve, or a guilt cycle waiting to happen? Both, depending on how it's framed.
"Cheat day" culture treats one day a week as a pressure release valve for an otherwise restrictive diet — eat "clean" for six days, then eat whatever you want on the seventh. It's popular, and it's worth examining honestly.
For very restrictive diets, a planned break can reduce the psychological burden of constant restriction and may help some people sustain the other six days longer. The structure and predictability seem to matter more than the specific mechanism.
Framing one day as "cheating" reinforces an all-or-nothing mindset — food is either allowed or forbidden, virtuous or sinful — that tends to produce guilt and, for some people, a binge-restrict cycle that's harder on both physical and mental wellbeing than a more moderate, consistent pattern would be.
There's no need for a release valve when nothing is forbidden in the first place. A big dinner out or a dessert you actually wanted nudges your daily score, and your 7-day rolling average absorbs it — no guilt framing required, because nothing was "cheated" on.
If you've built your eating around strict rules and a weekly release valve, it might be worth asking whether the rules — not your willpower — are the actual problem.