Hopefully, at some point, every man is gonna break down a whole fish. Ideally, you’d catch it yourself, but perhaps a friend or neighbor may drop one off for you to enjoy. But, really, you’re gonna catch one at some point, or be on a camping trip when someone else does, and you get to be the guy that says, “oh yeah, I know what to do with that.”
Food 52 has a nice clean introduction to the process. They go through gutting and scaling, so you can roast or pan sear it whole.
You could definitely take the next step and fillet it here, but when you’ve got a fresh caught whole fish, why would you do a thing like that?