Hitting snooze repeatedly fragments the final stretch of a night's sleep, which is disproportionately REM-rich — the stage tied to memory consolidation and emotional processing (see Deep Sleep vs REM Sleep: Distinct Recovery Functions). Dr. Cheri Mah's rule: if you use snooze at all, use it once, for about 5 minutes, then get up — rather than cycling through multiple snooze intervals, each of which interrupts a fresh, shallow re-entry into sleep without delivering any restorative benefit.
The reason to cap snoozing at once rather than treat it as harmless: repeated snooze-button presses specifically fragment the final stretch of the night's sleep, which is disproportionately REM-dense (see Deep Sleep vs REM Sleep: Distinct Recovery Functions) and tied to memory and skill consolidation. Each interrupted micro-cycle degrades that consolidation window rather than simply subtracting a few minutes of generic "sleep," which is why the guidance is framed as a hard cap rather than a soft preference.