Additionally, there are many situations where PPC (a component of SEM) makes more sense than SEO. For example, if you are first launching a site and you want immediate visibility, it is a good idea to create a PPC campaign because it takes less time than SEO, but it would be unwise to strictly work with PPC and not even touch search engine optimization.
This relationship between rankings and clicks (and traffic) is strongest amongst the top 3 search results. However, changing layout of the search results pages is constantly changing, with the inclusion of Google’s Knowledge Graph data and the integration of Universal Search elements (SERP Features) like videos, maps and Google Shopping ads. These developments can mean that the top 3 organic rankings are no longer the 3 best positions on the SERP. This has been demonstrated in heatmap and eye-tracking tests.