As a avid Fisher dedicated to catching all the big fish in the game I use it to blow apart everything I catch, and while this provides a stream of things to sell for a few gil the big win is that it gives me tons of water clusters, and crystals which when sold in reasonable sized stacks generate a nice income. It's not going got make me a gillionair but it lets me buy the odd minion or materia for melding.

There are also a few pieces of glamor swimwear and a minion that can sell for a bit also.

Now it's not as profitable a desynth as others are. But since I have all these fish it makes sense for me.