>>106939355
Backups that don't take much space and are done instantly.
The way distros like openSUSE or CachyOS set these up by default, anything in your system (not your home folder) gets backups. Whenever you install or remove something, a backup is done. If you mess up, you can revert back to a previous state quite easily with a command.
If your system doesn't boot properly, but you can access the bootloader, you can choose one of those snapshots, boot from it in a state that's read-only (so you can't make any changes, it's just to check it works) and if you're satisfied with it, use a command to use that snapshot once you reboot. But this has to be setup fairly manually in different distros, while these two I mentioned set them up for you. So when you install let's say, GNOME alongside KDE, and you think it's bullshit and you don't like it, but you can't be bothered to check what packages GNOME installed and it's all a convoluted mess, you can just revert to the snapshot created before it got installed and there you go, all you'd need to do is delete a bunch of config files in your home folder, sometimes not even that.
>Can't I just do normal backups any other way
Yep, but not as fast, not as compressed. btrfs has a few advantages over ext4 but I think the best reason to use it is this.