Well, if you plan to raise any pets and don't won't to buy the crown snacks, craftable snacks tend to be a little cheaper in the long run. You can also make furniture for your house. In general, though, it's not important.
You don't HAVE to craft. It's totally optional. But once you complete each level of crafting, you are able to buy recipes for crafting treasure cards from your main school, housing items and gear. Some people craft items to sell for gold at the Bazaar. Some like the challenge of it, as many items are very difficult to collect all the reagents for. I like it because it gives different goals from just "defeat ___ of ______" or "talk to ____." As you are running all over the Spiral, it gives you something to keep an eye out for, whether you need the reagent or will just sell it at the Bazaar -- even 3 gold for the common reagent is 3 gold you didn't have before, and the rarest reagents are worth way more.