I am making good use of Shotwell's duplicate finding function to sort out 15 years worth of messy photos. Starting with a blank slate, and importing photos one folder at a time, so it will only copy one of each photo into my Pictures folder.
All this because I spent five years juggling external harddrives with a small harddrive on a Macbook Air (never again with the small hard drive!). Now those days are over, and there is hope.