With SEO it’s all about the cache. Crawl frequency determines how changes impact your site. Without an updated cache, there are no significant changes or rankings to report to search engines.
Do you see why getting the attention of spiders is important? They are the gatekeepers between your content and the world. RSS is one method to toggle spidering, social bookmarking is another, but the fastest way to increase your cache rate for content is to (1) increase posting through using consistent time periods to introduce new posts or pages and (2) build inbound links to internal pages to create spike in network activity necessary to attract the spiders (otherwise known as a ping). Pings from your site are a digital invitation to search engines update changes.
With each data center (an aggregate number of computers used for storage and data retrieval) on its own schedule, it is the collaborated and compiled collective snapshot your site averages across multiple checkpoints, based on the search engines algorithm, the weight of the inbound links and how they aggregate link weight and popularity (see the definition of Page Rank).
Sergey Brin and Lawrence Page the founders and brilliant minds behind the Google search engine define the page rank algorithm in detail. The referenced in the link above is a PDF document, so you can also print it out in the event that you want to study it in greater detail.
In addition to page rank being a method to assess the importance and popularity of how search engines view your site, a higher page rank implies your site is a resource and it well withing boundaries of the guidelines. Additionally, pages with higher page rank are spidered and indexed more frequently, which if coupled with a content development strategy can expedite website authority for your content.
Before even stepping beyond the threshold into optimization, the first thing an SEO assesses is the crawl rate of your topical content and your deeper sub folders of your site. Removing obstacles that impede crawling are like pulling the weeds from the roots of your site that are vital to getting valuable search traffic.
If you had to break SEO into pieces (which it is) since search engines are based upon layers of coherent systems, redundancy, inquiry and execution, the cache is the starting point for search engines and SEO as well as a vital gatekeeper that determines the initial and continued pursuit of relevance and order. Hat’s off to search engine spiders for their silent yet crucial role in crawling, indexing and creating structure on the web without them there would be no search index to share.