Since heading tags typically make text contained in them larger than normal text on the page, this is a visual cue to users that this text is important and could help them understand something about the type of content underneath the heading text. Multiple heading sizes used in order create a hierarchical structure for your content, making it easier for users to navigate through your document.
Excellent post Brian. I think the point about writing content that appeals to influencers in spot on. Could you recommend some good, manual strategies through which I can spot influencers in boring niches *B2B* where influencers are not really talking much online? Is it a good idea to rely on newspaper articles to a feel for what a particular industry is talking about? Would love to hear your thoughts on that.