Fedora 16 to use Btrfs as its default filesystem

Part of the answer is just that maintaining an overall "how much space have we wasted number" is yet another metric to store and maintain, and it does tend to get tricky to count in the face of snapshots. So there's a real CPU cost involved.

But the main reason is that I prefer the filesystem be predictable. If your file size is less than a specific value, it goes into the btree. It's very simple to explain and isn't surprising ;)