What a single high-calorie meal actually does
A one-off large meal during a diet has a few real physiological effects. It refills muscle and liver glycogen, which can restore training performance and a fuller muscle appearance, and it produces a transient rise in the satiety hormone leptin, which tends to fall during prolonged calorie restriction. Much of the immediate scale jump afterward is water bound to that new glycogen and to sodium, not fat.
These effects are short-lived. The leptin bump from a single meal lasts hours, not days, so the idea that one cheat meal resets a suppressed metabolism is overstated.
Weighing the cost against the benefit
In strict energy terms, a large surplus meal offsets roughly a day of accumulated deficit, which is minor against a week of dieting. The more useful framing is psychological: a planned higher-calorie meal can improve diet adherence for some people, while for others it triggers a loss of control that does more harm than good.
Responses to flexible dieting strategies are individual, and people with disordered eating histories may find cheat-meal framing counterproductive. This is general educational information, not medical advice; a qualified professional can help tailor an approach.