That's one goal of proving a theorem. It's still useful to know the answer ahead of time if you're going to prove it. And some stuff is useful to know anyway. Proving P = NP would be super important to know, even if no one actually understood why. In fact, there's countless theorems that depend on results which have not been proven yet. People may have been doing important work that relies on the Riemann Hypothesis because they incorrectly believed it was true and that time might have been wasted. Additionally, once you find a proof through exhaustive search, it's entirely possible that human beings can go in there and simplify it to a level that can be understood by people. And maybe multiple results might paint a picture that shows us a direction to go in that we wouldn't have guessed beforehand.