It's possible for data to accumulate in the annex that no files point to
anymore. One way it can happen is if you `git rm` a file without 
first calling `git annex drop`. And, when you modify an annexed file, the old
content of the file remains in the annex. Another way is when migrating
between key-value [[backends|backend]].

This might be historical data you want to preserve, so git-annex defaults to
preserving it. So from time to time, you may want to check for such data and
eliminate it to save space.

	# git annex unused
	unused . (checking for unused data...) 
	  Some annexed data is no longer used by any files in the repository.
	    NUMBER  KEY
	    1       WORM-s3-m1289672605--file
	    2       WORM-s14-m1289672605--file
	  (To see where data was previously used, try: git log --stat -S'KEY')
	  (To remove unwanted data: git-annex dropunused NUMBER)
	ok

After running `git annex unused`, you can follow the instructions to examine
the history of files that used the data, and if you decide you don't need that
data anymore, you can easily remove it:

	# git annex dropunused 1
	dropunused 1 ok

Hint: To drop a lot of unused data, use a command like this:

	# git annex dropunused `seq 1 1000`