I've got a 480 GB SSD in a MacBook Pro running OS X El Capitan 10.11.6. I have recently reformatted the drive and clean installed the OS.
I have very limited programmes installed on this machine and all my files are managed by Dropbox, using their smart sync feature, which stores all your files in the Dropbox cloud and downloads them locally as and when you need them.
What's strange is that although I've got a 480 GB SSD, and only using c. 25GB as confirmed by the total at the bottom of Finder (see attached screenshot), if I go to About this Mac → Storage, it says I've used about 210 GB, mostly all photos and movies.
Any idea why this would be?