Basically, template compiling. Not having to copy/paste reusable parts around, which is error prone and time consuming. Depending on the tool there's other stuf

Basically, template compiling. Not having to copy/paste reusable parts around, which is error prone and time consuming. Depending on the tool there's other stuff, like generating sitemaps, optimizing images, CSS treeshaking and other optimizations, all the good stuff that would otherwise happen manually or not at all.