As a web dev myself, I wanted to add to that that Google’s Page Speed insights are sometimes a little misleading or at least have to be interpreted and taken with a grain of salt. Sure, a site / web app might be marked as slow because certain thresholds aren’t met, without the user even noticing that the app is “slow”.

As an example, apps which load in lots of third party content. As a user, you would expect them to have this slight delay when opening and will be fine with it without perceiving it as slow.

It’s really more important for marketing websites because google will rank your page worse when it perceives the page as slow.