|A pretty butterfly. Hurm.|
Roleplaying your alignment is sitting down and acting out your guy, and, by the way, your guy acts like this. If this decision is important enough to control how you play this character forever then this major philosophical crossroads would be where these games spend the bulk of their character generation time. It's a second set of Who You Are and What You Do. It's not useless information but it does lead to things like the cliché of the paladin and the thief falling out with one another.
Now your classic AD&D-and-onward alignment schema, the 9-panel-grid, complicates things by throwing in things further when some of the alignments are separated by thin conceptual membranes, using arbitrary assignments of Good and Evil, and leaves absolutely no room for moral relativism. It's a coloring book situation, and you'd better not go outside the lines, and by the way if you're True Neutral you should really use green for that.
If anything undercuts any usefulness of alignment it's the internet. Do an image search for alignment charts and you'll discover that Orcus, demon prince of the undead, bat-warthog-man-god who drinks soup made of hair and blood on a throne made out of baby skulls, is JUST AS EVIL as Microsoft Internet Explorer, which did totally bork your computer that one time. When you apply a gradient to morality but don't allow for any middle ground, or worse rigidly categorize a midground making it therefore not a gray area, you end up with these kinds of situations, and seeing how people feel about these alignment descriptions in graphic form kind of takes a bit of menace out of the idea of evil. And when evil isn't even scary or particularly effective (did you know Always Sunny In Philadelphia is worse than actual demons who shit in virgins?) the question of good versus evil becomes more of a question of who cares.
I ignore the shit out of that, but I use alignment all the time. In three ways.
The first and most pervasive is reputation. This is the nine-panel grid above but doesn't implicitly or explicitly restrict player behavior, or even player behavior when people are watching. Your reputation is just how people expect you to behave. Even a saint might find it convenient to be thought a devil, just as a wolf wears sheep's clothes. If you act differently than people expect, their impression of you changes. This is how it works in all fiction. This is how it works in real life. Accepting payment from the government for a job well done should not bork your slightly-too-close-anyway-now-you-mention relationship with your deity, but people will absolutely start to get the word that you're not exactly living a spartan lifestyle if you keep it up.
The second is the B/X alignment system, which only has 3 alignments. Really, it only has two alignments, Law and Chaos. If you want society to keep going because society makes things you like such as warm beds and sewers and some of that stuff is worth the occasional tax or church service, that's Law. If you want to supplant the law, but to supplant it with your own law, because you think you'd be a more just ruler, that's law. If you want to get up, go to work, go to bed, that's law. If you want to be properly paid for clearing out those chaotic fucking caves like you promised, or want to study hard to become a good magician, or assent to giving up pork for Lent, that's Law. Most motivations we have are Law, even some of the selfish ones. Chaos is specifically being Anti-Law. You want to strike down the gods, because who are these gods anyway? You want to rape the horses because they're there. You want to sack the kingdom because you want to get drunk. You sell your soul to be a good magician, and you want to be a good magician because you want the awesome things you get with that. Law is about You And Your World, Chaos is about You. Neutral means you fuck off from polite society and find your own way but you're not a huge fucking dick about it and don't burn down any forests just because you can, or because you're ordered to. Self-Sacrifice, Self-Reliance, and Self-Interest, if you like. The players don't pick this. To a large extent, I pick this. If we're running a game about conquering the known kingdoms and leaving a razed land in our wake, or if we're about people who find themselves united in the dark on an endless dungeon crawl, those are specific games. Most of the time, however, the PCs have a somewhat vested interested in the world's infrastructure if only so their money can be spent, so they default to Law.
The third is specific to Arcis Enumre and it's physical vibration. The world is made up of spiritual matter, physical matter, and magical matter. These are three great sheets in the obsidian chunk of the world. Everything has a composition such as this to one extent or another, including people. Remember, I'm not talking about different dimensions. Rather, someone aligned with the magical plane exists in the same world as someone aligned with the physical plane, but they experience the world fantastically differently. This is where things like protection spells make a lot of sense to me. This is where things like alignment languages, and switching alignment languages one a dime if you switch alignments, or hell switching alignments as a gameplay decision rather than a natural progression of a story, all make sense to me. It's all about harmonic vibration. Elves have no connection to the spiritual world whatsoever, and so don't dream, don't have souls, and are supremely aligned with the magical world. Clerics and Magic Users are aligned with sympathetic vibrations from spiritual and arcane planes, and most average everyday villagers are by default associated largely with the physical spectrum.
This makes us have another 9-panel-grid, of course: lawful spiritual, lawful physical, lawful magical, etc. It's descriptive, though, not prescriptive, and defines context for your adventure and bodily aspects of your character rather than How To Play Your Guy.
I'm not saying it's way better but between this and Reputation, I like it a lot better. Especially since its chief virtue is that the only person at the table who has to actually give a shit about alignment is ME, the DM, and even then only just a little.