If you were just putting on a new chain in the comfort of your home, now got an old worn chain to reuse! Since you know how to remove links and reattach the segments, you can use part of the old chain as a cable to lock your seat onto your bike. This is very handy in urban areas.
You can also make yourself a bike chain bracelet or an earring. You'll need a fairly big piercing and a tough ear to get that stud through.