In an ideal world, the search engines would be able to find and understand all content anywhere on the web and return relevant results for your search regardless of technical considerations. The web is a technical platform, however, and there are correct and incorrect ways of building websites. Certain kinds of issues can render your website invisible to the search engines, making it less likely to rank well and provide a great user experience.
While some of these issues are caused by errors or mistakes which should clearly be avoided, others arise from simply choosing certain ways of presenting content that would not necessarily be “incorrect” in a strict web development sense.
In order to be an effective SEO, it’s critically important that you understand how search engines discover, understand and rank web pages from a technical perspective. This will help you with diagnosing inevitable problems, improving existing websites and specifying high performance redesigns or fresh builds.