From the official Google Webmaster Blog:
“People want to be able to find answers to their questions as fast as possible — studies show that people really care about the speed of a page. Although speed has been used in ranking for some time, that signal was focused on desktop searches. Today we’re announcing that starting in July 2018, page speed will be a ranking factor for mobile searches.
“The “Speed Update,” as we’re calling it, will only affect pages that deliver the slowest experience to users and will only affect a small percentage of queries. It applies the same standard to all pages, regardless of the technology used to build the page. The intent of the search query is still a very strong signal, so a slow page may still rank highly if it has great, relevant content.”
An important message is the part about “great, relevant content”! This is an important indicator for well coded, well written and semantical content. This benefits not only the search engine results but accessibility as well.
Read more about this change.