Comment # 22 on bug 1165780 from Karl Mistelberger

(In reply to Franck Bui from comment #18)
> Also what's the point of enabling the service unit if the path unit is
> supposed to automatically trigger it ?

Settings are:

erlangen:~ # systemctl list-unit-files btrfsmaintenance-refresh.*
UNIT FILE                        STATE   
btrfsmaintenance-refresh.path    enabled 
btrfsmaintenance-refresh.service disabled

2 unit files listed.
erlangen:~ # 

btrfsmaintenance-refresh.path watches for changes of
/etc/default/btrfsmaintenance and fires btrfsmaintenance-refresh.service if one
is detected. IIRC defaults don't work.