When you make something with code, you're probably used to figuring out a design as you go. You write a function, you choose some arguments, and if you don't like what you see, perhaps you add a new argument to that function and test again. This cowboy coding as some people like to call it can be great fun! It allows systems to emerge more organically, as you iteratively see your front-end design emerge, the design of your implementation emerges too, co-evolving with how you're feeling about the final product.