All it does is convert .md files to .html and optionally uses nested Golang templates. There are some tricks behind the scenes, like support for tags and meta data (just like regular static site generators). Flexibility is concentrated into the templates, so no other files are needed.
I think the content (files) should reflect the structure of the webpage as close as possible when using a static site generator. When reducing complexity, we can go all the way down to the filesystem, where files and directories are the main building blocks. Content and design must be separated as much as possible.
I have not tested all static site generators out there, but the few that I tried did not satisfy my demands. So I just made my own (for fun and learning).