Best Practice for Templating-Workflow, coming from static HTML
We used to do what you are doing, for a good many years - it was especially helpful when we didn't know what CMS we were going to use yet, or when we had a front end specialist (hello) who would send the files off to the back end specialist for implementation.

However, with Craft, we've found that the front-end people can use it well enough to not need a 'back end specialist', so we find ourselves no longer doing site builds as front-end assets first. It's just faster and easier to build the HTML/CSS/JS from inside the Craft templates.

We also used to (and still do for larger projects) build a completely non-styled "blueprint" of the website. The objective was to ensure that the site structure was correct - here's an example: http://example.bp.myvcsite.com/

That was/is part of our whole approach where we split things into blueprint; visuals; static build; CMS integration: http://example.myvcsite.com/