[Meads]

+d makes sure, all files that are used in the session are being displayed in the clip list (due to a search it might be, that only a selection is shown, and the following command only applies to those, that are being displayed in the list).

+u selects all visible files in the clip list, that are not currently used in the timeline.

+b lets you select if you only want to remove these files from the session, or if you want to delete them from your drive as well.

You can select all those options from the little arrow to the top right of the clip list as well.