If you’ve bought a new Mac in recent years, chances are it arrived with flash storage in place of a traditional hard drive. In terms of reliability and rapid-fire boot times, flash storage is awesome, but it’s expensive. So to make it more affordable, you don’t get the capacity you see with hard drives.
There are a lot of ways to work around the built-in limited flash storage, but there’s another method for eking out a little more space: Purging duplicate files. Few of us bother doing it, because weeding out extra copies of photos, documents, and other media simply takes too much time and energy.