Previously, Google's "Speed Update" was only a factor for desktop users. Fast-loading pages was always a recommendation for mobile sites, however, it was never used in ranking on Google. Now, speed at which a piece of content loads plays a factor in search results.
This new update is most important for website owners and SEOs to take into consideration. Also worth noting is that Google has said this update will only affect the slowest of mobile sites.
However, this update will not prevent slow loading mobile sites from showing up in Google rankings, because if a slow loading page happens to contain the most relevant content to a user, it may still rank in search results. Relevancy will always be key.