I can see how there might be usecases for stuff like this in big enterprise developments that change their design often and/or have lots of different departments of people working on the site, but in all the webdev I have ever done myself in my almost 30 years of work in it, I have never had any need for more than hand-written html, css and javascript. That and simple template systems like django/jinja have worked quite well for me and always perform far better than these big frameworks.