Humans can extract information quicker from proper layouts. A good layout brings faster clarity in your head. What developers often get wrong: it's not just about doing something, it's also about how simple and fast to parse and understand it was (from a visual point of view as well, of course information architecture and UX matter a lot as well). Not aligning things is a slippery slope. If you can't center a div, probably all the other things that are more complex in your website / app are going to be off or even broken. Thankfully AIs can center divs by now, but proper grid systems understanding is at best frontier.