Seriously, how many reasons do you need?
It's cool in the evenings. It looks awesome with shorts. It looks awesome with pants. It's nice to have a hoody after the beach. You can't go camping without a hoody. Hoodies bring happiness. It is a lucky hoody. You can wear it after you play ball. Chicks dig it. There are a buzillion arguments for wearing the DC Reason Full-Zip Hooded Sweatshirt, but for sanity's sake, this is only an abbreviated list.