Gary Illyes from Google says that have included mobile page speed in the "Mobile First Indexing"
If you want to sell online, your shop needs to be fast! Speed is particularly important for mobile phone users. - If your shop is slow, customers buy from your competitor.
And if that isn't bad enough:
Like most other shop platforms, Shopify struggles to perform on mobile. This can be costly, especially if you sell to the 64% of people in the western world who own a smartphone. Fortunately there is a solution.
Using PageSpeed Guru is simple. Just click the optimize button. Wait for 1 minute and you are done!