The main reason is flexibility.One day your boss stands next to you and asks: "can you move this border three pixels to the left", and the only correct answer is "but that requires a complete rewrite".
I am reminded of <a href="https://xkcd.com/1425/" rel="nofollow">https://xkcd.com/1425/
amelius · · focus · HN ↗
One day your boss stands next to you and asks: "can you move this border three pixels to the left", and the only correct answer is "but that requires a complete rewrite".
Kerrick · · focus · HN ↗