Relevancy in Google’s eyes begins with strong content. Furthermore, that same content needs to be well structured. One of the best ways to inject positive results into your organic campaign, is to structure your website into a symmetrical organization – silo structuring.
A disjointed website will many times wreak havoc and minimize the keyword performance of your site. On the other hand, if you tightly theme your content, search engines will index your site better and give you a boost in keyword rankings.
A clean site structure is clearly one of the most powerful and underrated SEO strategies today.
Website Siloing: An SEO Strategy For Optimal Results | WebProNews

Very interesting theory, what do you think about the silo structuring?