Basic usage for managing btrfs filesystems.
To view filesystem usage:
sudo btrfs filesystem usage /
To see which partitions belong to a file system:
sudo btrfs dev usage /
To list snapshots (subvolumes):
sudo btrfs subvolume list -s /
To list snapshots taken by apt-btrfs-snapshot:
sudo apt-btrfs-snapshot list
To remove all the snapshots:
sudo apt-btrfs-snapshot delete-older-than 0d