Do you use first level headings in MarkDown documents? And if yes, how do you use them?

Somehow I feel it's only for document titles, so because it's redundant with the filename I don't use it unless several documents are compounded into one file. I sometimes use it for anything that isn't a title but that's of a chigher level than a chapter, like parts, but it's so rare to use them…

So I end up never using first level headings in MarkDown, and in HTML it's only for the the site's title.