As internet grow, it already gains some history and search engine optimization has history as well. At the beginning SEO was a wild west zone. Pure mechanical number of links and keywords on a page moved sites high in ranking. Google replayed with Panda, Penguin and Hummingbird algorithm updates to wave away sites with spam content. Now old days practices would be considered as bad, outdated and harmful. The term SEO expended to a range from white to black techniques with large gray aria. There are different search engines with therefore different algorithms. And after all website are created for people not search engines. SEO professional is very well aware of different practices and will recommend staying away from “black” practices and for the “gray” zone should be clear understanding of what is done and for what purpose, what are the pros and cons. It is truly a lot to do in “white” zone and that work might be most rewording in the future.