I installed openSUSE Leap 42.2 with btrfs as root. Now, performing a btrfs
balance or a snapper cleanup takes "ages" while there is no or little disk
activity but btrfs or btrfs-transaction constantly hogs one CPU. There is
plenty of unallocated space (28 out of 40 GiB). 

The system becomes very unresponsive and even loses its WiFi connection until
next reboot. Thus, btrfsmaintenance will nearly kill my system every week!

After disabling btrfs quota everything works fine! Thus, enabling the
experimental btrfs quota feature for snapper was a really, really bad idea.
IMHO this is critical bug, if it happens to other user.