There is a thin line between optimizing a website for search engines and optimizing it for users. In order to get the content and keywords onto a page that are necessary to boost search engine rankings, it is often the case that usability is compromised. If your page is totally optimized for search engines, but compromises usability, you may be able to drive a lot of traffic to the page, but only convert a small amount of it. On the other hand, if you optimize the page only for usability, leaving off loads of content, you may be able to better convert the traffic that comes, but there will be far less traffic.
A good way to find the best balance is analyzing your analytics. In Google Analytics, for example, you can set up goals used to track conversion on the website. Test your goals on different pages. Optimize a page for search engines and track conversions on that page. Optimize another page for the users and track the same conversions on that page, but as a separate goal. This will let you see if you generate more conversions from the search engine optimized page, which should generate a high amount of traffic with a low conversion rate, or from the user optimized page that should generate a smaller amount of traffic but a higher conversion rate.
