One downside might be that if the next person (person N+1) doesn't know the system and just edits the HTML and CSS by hand for a few months or years, and then p

One downside might be that if the next person (person N+1) doesn't know the system and just edits the HTML and CSS by hand for a few months or years, and then person N+k comes along and runs the generate script, he potentially blows away any edits that weren't done with markdown and the site generator. I suppose you could use the static generator for the initial build and then throw it all away yourself, but that's basically the same as not using it at all.