Your site can be easy to navigate for consumers, but is it easy to navigate for search engines? Not all sites take into consideration the affect that certain site structures have on the bots that crawl your site nightly, or at least frequently. Make it too difficult, and they might not visit as often. Make it easy and you may find that your pages get indexed quickly and more of them get indexed.
What we are referring to is something called siloing. Think of a silo that you might see in a farmer’s field. The silo has layer upon layer of corn or another crop. All corn, just stacked up one kernel on top of another until the top of the silo is reached and it can’t hold any more.
To know what is in the silo you don’t have to dig down to make sure that every kernel is a corn kernel. You know from looking at the top that the entire silo is filled with corn. A website silo accomplishes the same thing: everything in the silo is related to the same subject. So if your silo is about kitchen cabinetry, then every page in that silo is about cabinets, the types of wood used, the types of hardware available, the cabinetry door profiles, how to construct a cabinet, how to hang a cabinet, installation techniques, and so on.
Each silo page links to the other pages in the silo. They all relate. So someone landing on a page about cabinetry hardware, might also want to know how to install that hardware, and voila! There is another page on the silo menu about installing cabinet pulls or hinges. If your site is organized in silos such as this, search engines have very little trouble figuring out what the silo is about, and what the pages are about. They see you have a lot of pages about this topic, they all relate thematically, the words used all relate to kitchen cabinetry in some way, and they give you “ranking credit” for the fact that you have made it easy for them and for searchers to find the information that they need.
The ranking benefit of this structure is that you really don’t have to rank all the pages one by one. Concentrate on the top of the silo and everything else should get the benefits of that link juice because they all share (because they are interlinked). This is a simplistic explanation of how it works, but the idea is that you have done your job with structure and quality, extensive content. You don’t have to work hard on every page, just the top page. Just like with a corn silo, you know what is inside just by looking at the very top layer.
Any confusion? Read this Moz article for a more in depth discussion.