When I migrated to SSD on my Mac mini, I kept the original 1 TB hard drive to store my old Mac OS data. That was just in the SSD migration failed. After two weeks of non-event, it was time to blow up my 1 TB hard drive. That means deleting the entire drive and using it as a backup drive for storing miscellaneous and less frequently accessed files. I’m not worried about the new SSD failing, because I have Time Machine. I can always restore the entire OS from my Time Machine backup. So, I dumped everything on the 1 TB drive and emptied the Trash Can. I took awhile, but now I have all that real estate for storage.