The SMBC comic is completely right. We don't need Superman fighting crimes. Police are geared to the teeth, they don't get persistently overpowered by criminals. In fact actual fighting crime is both the least interesting least difficult part of it. The trick is finding out whose committing crimes, finding out where crimes are being committed and changing society so less crimes are committed overall. Superman is actually not much better equipped to deal with any of this stuff than any other clever guy. About his only useful crime-fighting ability is that his superspeed would allow him to have really quick 999 responses. But we've already got response times of 10-15 minutes and the overall affect Superman could have would be really low.
So really the best effect Superman could have would be environmental/energy related, you'd stick him in a giant treadmill or whatever and get him to generate electricity. Except I'm not sure how effective he would be at that, he runs fast but does he run fast enough to out perform nuclear fission? His heat vision at the very least is nowhere near up to snuff. If superman is immortal it would be worth doing it just to be thermodynamics which would be interesting.
But all this stuff even still probably isn't too effective. We already have plenty of food in the world to satisfy everyone for example, it's just a distribution problem through human greed. Assuming Superman is lawful good and doesn't descend to stealing food from us and giving it to starving people (and wow he would need even more entertainment than us to distract himself from that problem if he doesn't. I don't know if his sense of justice would survive). If someone backed him with enough capital he could single handedly run a massive farm and give/sell cheaply the produce to countries suffering famine. But again, I'm not sure if his savings in labour are anything like the burdens of trying to raise enough money to buy enough land to implement that. I suspect the venture capitalist is far more vital there than Superman.
So if Superman is incapable of having sufficient effect on the world to noticably save lives to anything like the extent say, Bill Gates does, what about military application?
I would say that Superman could well be a detrimental effect even to war. He could single handedly win any battle, but even with his super speed, he's probably not fast enough to singlehandedly stop a large multi-pronged co-ordinated attack and hes almost certainly not fast enough to stop a nuclear bombardment from a major player. His presence would mean that in any war he was involved in, the opposition would have no chance to win a convential battle so would immediately have to turn to mass bombing of civilain populations or nuclear warfare.
His benefits would be in very small countries with only a handful of nuclear weapons. We could perform a strike on the country and rely on Superman to catch the nukes. This does rely on us having exact intel on where the nukes will be launched and providing him with it, but that should be possible.
So in conclusion, the superhero genre exists as a way of making it feel like the worlds problems are easy to solve by reducing the problem to a simplistic 'punch bad guys'. This doesn't work in real life and it would require a lot of intelligence to work out a way where Superman could really benefit people, it most certainly wouldn't be fighting crime, but there could be some tactical war advantages or environmental benefits, depending on the capacity of his abilities
