As a result of GoogleSpeed Optimization Service you will get at least 80/100 score both for mobile and desktop devices. This score will give you positive rate and your pagge will be marked as a website that applies most peformance best practices and should deliver good user experience.
Google's PageSpeed score is important for website SEO value.
Google has recently gone on record saying that page speed will be a ranking factor in its upcoming mobile-first index. Details on how they will evaluate page speed for mobile and calculate rankings are still unknown. But, what we do know doesn’t change much from what we at Yoast have been saying for some time: make sure your site is responsive, as fast as possible, solidly structured, and full of excellent content.