It is very important to know How search engines use links.
The search engines use links primarily to discover the web pages and to count the links as a votes for those web pages.
How Search Engines Use Links :
Search Engines needs to decide which page to include in their index. Crawling the web is one way to discover the web page. Another is through the use of sitemap xml . Search Engines do not include pages that they intent to be very low value. As this will not lead to good user experience.
Crawl Rate and Frequency
Search engines spiders crawl a portion of web page every day to fetch results . It starts with deciding where to begin and where to go. Google has publicly indicated that it starts its crawl in reverse Page Rank order. Its crawls Page Rank 10 sites first, then Page Rank 9 site and so on. Higher page rank site are crawled more deeply than other sites. This is because the changes on the most important sites are the ones which search engines wants to discover first. If a very important site links to the new resource then it will tend to place a lot of trust on that new resource and factor the new link or vote into their algorithm very soon.
Links play a vital role in ranking. Consider two sites where the on page content is equally relevant to a given topic but that site does not have trustworthy link to other important site then it will rank less than the site which has link to one of the important site. So the site which has link to more important site will be more likely to rank on higher side in search algorithms.