I keep some cichlids and they often nip the fins of others when breeding, so I often put some melafix in after a water change to help them heal up quicker. Also, I think it makes the tank smell really, really nice as an added extra!
Other than that I don't have anything extra. For awhile when I set up my new tank I had a few white spot outbreaks so I kept some of that treatment to hand, but haven't had to use it fr a long time now. And the other poster is right, they do go off after awhile and they are too expensive IMO to always have them 'just in case'.