A/B testing possibilities
Testing two or more versions of titles, URLs, images, or articles is a challenging part of SEO because it is not always possible to accurately declare the winner. The main obstacles are above all the long time range needed for seeing the results, seasonalities and the inability to assign the impact to a specific change in time (e.i. due to the neverending algorithm updates). On top of that, Google is trying to only display one page per domain in SERP which makes creating two versions of one page meaningless. In the case of PPC, however, most of these obstacles are eliminated and it is possible to test a large range of elements over a condensed period of time with relatively high reliability of impact attribution.