This is a "housekeeping" operation. Normally, all audio recorded within a project remains on the hard drive, but Purge Audio Files allows you to remove files which are not actually used in the project. This utility looks at every region used in every playlist (version) associated with the project, generates a list of audio files that do not appear in any playlist, and invites you to delete all, or selected files on the "unused audio file" list.

This is a destructive process, so don't use it until you're near the end of a project or are very sure that the outake is really so bad that you don't want to use any part of it.