Since you mentioned complexity, past a certain level of application complexity, you realistically can't do a linear list of Javascript files that you import on the page in order. When you have hundreds of views, you don't want to manually go and figure out what each of them needs as prerequisites. Circular dependencies are annoying when you do it by hand but practically trivial with a packer as long as they're logically sound. Inversion of Control. On-demand loading. These are all problems that have been previously solved by hand, but when you don't want to solve these prerequisite problems before your actual business (or hacking) problems, you build tools to do it for you.