Today I was going through my drive with DaisyDisk to see what was taking up large amounts of space on my relatively small SDD hard drive. One culprit was the folder: /Users/Jonathan/Library/Application Support/Adobe/Common/Media Cache Files
Some of the files in here were close to 2 gb in size. Adobe has the following to say about these files:
When Premiere Pro imports video and audio in some formats, it processes and caches versions of these items that it can readily access when generating previews. Imported audio files are each conformed to a new .cfa file, and MPEG files are indexed to a new .mpgindex file. The media cache greatly improves performance for previews, because the video and audio items do not need to be reprocessed for each preview.
When you first import a file, you may experience a delay while the media is being processed and cached.
A database retains links to each of the cached media files. This media cache database is shared with Adobe Media Encoder, After Effects, Premiere Pro, Encore, and Soundbooth, so each of these applications can each read from and write to the same set of cached media files. If you change the location of the database from within any of these applications, the location is updated for the other applications, too. Each application can use its own cache folder, but the same database keeps track of them.
Choose Edit > Preferences > Media (Windows) or Premiere Pro > Preferences > Media (Mac OS), and do one of the following:
To move the media cache or the media cache database, click the respective Browse, button.
To remove conformed and indexed files from the cache and to remove their entries from the database, click Clean. This command only removes files associated with footage items for which the source file is no longer available.
Before clicking the Clean button, make sure that any storage devices that contain your currently used source media are connected to your computer. If footage is determined to be missing because the storage device on which it is located is not connected, the associated files in the media cache is removed. This removal results in the need to reconform or reindex the footage when you attempt to use the footage later.
Cleaning the database and cache with the Clean button does not remove files that are associated with footage items for which the source files are still available. To manually remove conformed files and index files, navigate to the media cache folder and delete the files.
I have put in bold blue the parts relevant to cleaning up these files. In my case using the Clean button only removed some of the files. Some very large files remained. So I deleted those manually. The key point is that it is safe to do so.