Why do developers/customers require layout with preprocessors or webpack/galp builders?

Question

Layout

From time to time I see announcements on freelance that you need to make up a particular project on pug preprocessors (why?) and on sass / scss, well, it’s clear there is a syntax for IE, as far as I know, developers need this to make it easier for themselves to make a project and more convenient how to me, but the customer needs a website, not a code. Enlighten me please)

Answer 1

The customer needs a website that will need to be maintained