I use that feature basically every morning. My alarm is only a backup for the roughly 3 times a year I oversleep. I hate waking up to an alarm which motivates me to get up before it goes off.
I have a home assistant automation that simulates a sunrise (not very well tbh, I need to get some dimmer bulbs) before my phone alarm goes off so I'm usually awake before it does. I use this feature almost every weekday.
If you use the sleeping settings, and wake up before your wake up alarm, it will prompt you “it seems you’re awake, do you want to cancel your upcoming alarm?”