These days I pretty much ignore the topics on the phpBB support board, but this one made me chuckle: https://www.phpbb.com/community/viewtopic.php?t=2230216
After thinking about it for a minute, though, I realized it would be worth making a couple comments about the use of Google Pagespeed to "optimize" your site.
One must remember that the first rule of business is to make a profit. Google happens to be quite good at this, and one reason is that people seem to blindly eat up everything Google serves to them (pun intended). For example, lots of people use their Chrome browser. I do not and will probably never do so. Why? If you read the fine print in the l-o-n-g agreement which is presented when you install Chrome, you will find that by agreeing to their terms, you have authorized Google to collect your browsing history and have Chrome covertly send it back to Google. I'm never going to agree to that! You may feel differently, but to me, Chrome is spyware.
Now, about Pagespeed Insights. Let's look at two of its "benchmarks".
It is no accident that Pagespeed Insights uses a 320x480 model for mobile...the 2:3 aspect ratio is the default for most Android/Chrome smartphones. If you follow their advice for tap targets, the resulting pages will look great on Android/Chrome smartphones but poorly spaced on iPhones (which have a 1:2 aspect ratio). Gee, er, um...do you think that was done on purpose?
The moral of this story is to remember that Google is in business to make money, NOT to make your sites run faster. Pagespeed Insights does contain a number of great suggestions to improve the page load times of your site, but it is clear that one of its main purposes is to make Google products look good at the expense of competitors' products.
There are many tools available to optimize page loading; it would be in your best interest to use at least two. It would also be in your best interest to check the results of the "optimization" on as many different devices/browsers as possible to insure the "optimization" does not cause problems with selected devices/browsers.
The Dion Designs Discussion Board gets a 98/Desktop and 92/Mobile score from Pagespeed Insights. It will never follow Google's advice for CSS loading and tap targets. I'm happy with that.