QUOTE: “Starting April 21 (2015), we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high-quality search results that are optimized for their devices”. GOOGLE
QUOTE: “There’s probably always gonna be a little bit of room for keyword research because you’re kind of providing those words to users. And even if search engines are trying to understand more than just those words, showing specific words to users can make it a little bit easier for them to understand what your pages are about and can sometimes drive a little bit of that conversion process. So I don’t see these things going away completely but I’m sure search engines will get better over time to understand more than just the words on a page.” John Mueller, Google 2020
The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.