Page Speed Checker makes use of the Google API "PageSpeed Insights". This means all scores you get, for mobile and desktop, will be real Google scores. If you have below 70 on mobile, you should really fix that for example. Google will not let you rank high on mobile search results then. And that's just one of the examples.
So it's important for your page(s) to keep scoring high. And why not have a nice history of these results too, so you can look back if things went downwards (for some reason). See what went well then and what doesn't now.. Compare these results and get your score(s) back up again!
You can take a look at the full details of this Add-On on the concrete5 marketplace. There are a couple screenshots there, full documentation on how to use the Add-On and how to retrieve the API key and such. All pretty simple to setup. Have fun!