A while ago, the fad went around the internet that content is king
! This meant that content was the most important aspect of your website. It attracts eyeballs and generates interest. If your content is consistently stellar, then people will consume it, spread it, and come back for more. Also, as seen in the link above, content is valuable to your SEO
because search engines can see what your site is about and categorize it appropriately.
Also, as people spread word about your fantastic content, the amount of links to your site floating around the web increases, showing search engines that people agree, your site IS the site to go to for information on animal husbandry or whatnot! Thus, content is king, but links are like currency
on the web. Not only that, its just good manners.
Links help your audience to easily find more information on something they have no idea about. It's also a form of credit, where you give other people their due for original content. Also, as I mentioned earlier, it helps search engines figure out which sites are more helpful when you need to know more about, say, cheese making. Otherwise, it's plagiarism.