Because links to a file from File Manager or Multimedia Manager may still be active even after a file is migrated to Resources, the file is not deleted in its original location. Since the files are in two locations, though, they will count twice against your disk-space allotment. A handful of files won’t make a big difference, but if you’re migrating entire folders or channels, the duplication could start to add up. Decide when you move each file whether you can go back and delete the original to save space.
Besides duplicates, also consider all the files that may be uploaded directly to Resources. With any number of people adding files, from other admins to constituents, it may be hard to manage what they’re uploading. Photos uploaded directly from a smartphone may be massive, and if there are dozens of them, you might be looking at a significant chunk of disk space. Make it a practice to monitor your disk space usage and clean up files that are too large or not being used. Resources has a filter to help you easily spot files that aren’t currently in use on your site.