People who are into affiliate marketing are constantly searching for keywords, which for their existing sites, when creating new content, for new affiliate projects., etc.
It's important to choose the right keywords to target the ones that will bring you on the site for buyers of the products you're advertising.
Long Tail Keywords are good KWs for sub-pages, and it's easier to point them than KWs where you have one or two words. You also target a targeted group of people who know what they are looking for, or ask questions on Google Search, and you have to answer them on your site.