Comment # 107 on bug 1063638 from Daniel Pecka

(In reply to Jeff Mahoney from comment #106)
> I agree that it doesn't need to be done automatically anymore.  It wasn't
> always situational.  It used to be that btrfs wouldn't clean up empty block
> groups, so once you used all of your storage, even if you cleaned it up, if
> your workload changed you'd be out of luck.  Balance also needs to be
> smarter about when it relocates.

exactly ... it was needed in past, so let's step ahead from past to present :)