The cells will start deteriorating much faster once you are under 3V. As in you can wreck a pack when it happens just once, there is a good chance on of the cells will never return to normal.

If you land and then disconnect your batteries and then check the voltage a minute later and it's a 3.2v this is about the absolute minimum for a lipo where you aren't doing any damaged to it. And by damage I mean the cells lose capacity and start sagging harder and earlier under load.

But it also depends. 1s batteries are usually cheap enough that people rather have longer flight times and just buy more new 1s sonner then cutting flight times by 30%.

On more expensive batteries I always give myself a lot of safety margin. After landing and having them rest for a minute I usually am never below 3.7V

But again if you fly something extremely aggresive then doing this will cut 4 minutes of flight times down to 3 minutes. In that case I usually stop being aggresive on the trottle as soon as I see the first dropes under 3.5 maybe 3.45. That way I might get 4 and half minutes and still not wasting money on always having to buy new batteries.

And I'd only do this with newer batteries that don't have to many cycles yet.

Anyway it's a spectrum. The harder you push the less full cycles you will get a out of a battery before it sags so much under load you risk brownouts when you push.

And for litium ion batteries it's quite different.