In addition to helping you manage external files, the external files manager allows you clear unused image sources/clips and unused materials from your scene.
To delete unused image sources and clips, click the Delete Unused Sources/Clips button in the Cleanup section.
This removes the source/clip pairs attached to any unused images, but does not delete the original images themselves.
To delete unused materials, click the Delete Unused Materials button in the Cleanup section.
This deletes all materials that are not assigned to any object in the scene, provided they are not stored in an external material library.
