Is there a way I can purge all unused files/assets via the file manager? I'd like to clean up some directories for a client? If not, is there a query I could use to find out which files are unused?

Is there a way I can purge all unused files/assets via the file manager? I'd like to clean up some directories for a client? If not, is there a query I could use to find out which files are unused?

UPDATE

Adding a little more context, the files are used with a number of add-ons:

1. Native file fields
2. Matrix
3. Wygwam