Sub titles are more important then the document title itself... before reading a chapter, 90% of people are looking at the chapters I am aksing myself if search engines can detect in-side-page chapaters Like a document could have Big title Intro .... Sub title 1 More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text Sub title 2 More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text Sub title 3 More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text More text Can search engines detect sub-titles?! in anyway... and if they can , do the allocate some importance to them?!
If you talking about the content on web page, the search engines take it all in, not matter it is the title, subheading or the small footer. Some people think that placing H1-6 tags around headings & subtitles have more influence. But that is still debatable. Placing keywords in your content is important, but the main thing is to get your message across to your audience, rather than having keyword rich content. For example, I am a web designer, I wouldnt write, "We are Web Design Specialists, We Design Designer Web Sites on the World Wide Web!" Your target audience will think you are an idiot for writing like that. Get your message to your audience first, then think SEO.
Using subtitles will help your user remain clear what they are reading, so dont worry about how it will affect SEO but allow your users to use your website with ease.
As a rule, I always use h1 tags, and h2 to sub-divide, and if needed, i'll go further. They are clearly good for the user, as they sub divide content in a logical way that most readers naturally understand. ...and for the record, I lean toward the side that says google likes/reads h1 and h2 text, and uses it for classification purposes. (figuring out which searches your particular site shoudl come up in the results for)
grobar... is you use h1 for titles, and h2 for subtitles and h6 for normal text, will search engines detect this as : title, subtitle and normal text?!