Imagine you’re a search engine spider and you're crawling through another webpage: your first stop is the website’s logo, then the menu and if it’s a behemoth of a website then there's going to be a pretty big menu to trawl through, then if you’re unlucky you’ll have a carousel of images - and you’ve still not reached the most important unique information yet!
Mainly the heading of the page, i.e. what that page is specifically about and then the content of the page to follow the heading - which should describe in more detail what that page is actually about.
This is run-of-the-mill stuff for search engine spiders, but really it shouldn’t be, because you can alter the positioning of the DIV tags from:
Navigation | Header | Content
Header | Content | Navigation
DIV order optimisation (this is a simplification) can definitely help in the optimising (SEO) of a website, naturally the DIV order won't do this all on its own, but as part of the mix that improves the indexing of a website.
And if you’re not convinced of this, ask yourself why all the pages on your website aren’t indexed; yes you can use the:
'rel="next" | rel="prev" | rel="canonical"
And this like DIV order optimisation is part of the SEO mix; which to sum up is basically the more you can do to improve the life of the search engine spiders visiting your, particularly e-commerce, website, the better performance from it you should expect and better performance usually means an increase in sales - which a lot of SEO practitioners seem to forget that this is what the website's there for in the first place.
At least that's my argument...