First of all: Big congratulations on your deal!
It is useful. For instance, I had to ride through a patch deep sand recently (on a Levo SL). It was virtually impossible for me to safely ride through it with the full length of the seat-post. On the second attempt (I was testing the Levo SL for sand-riding capability), I dropped the seat halfway, and could securely ride through the sand. Also, downhill rides are fun if you totally drop the seat, stand on the pedals and move your butt above the rear wheel

Getting on and off the bike with the seat dropped just means comfort.