I used it when my oranda got tail rot. It seemed like it helped speed up the healing process... I'm pretty sure it's the fishy version of bactine. The fish acted like it stung a little and then it was fine. Boy, does that stuff smell nice! (I think it's a love it or hate it thing, though...) It causes foam on top of your water, so don't be alarmed...
My vote? It's a good thing to have in your fishy medicine cabinet.