“Slow” is a powerfully repellant word. People hate to wait. We’ll visit a site less often if it’s slower than a competitor by just 250 milliseconds. This behaviour is hardwired, and it’s unlikely to change. And as one survey from Tealeaf/Harris Interactive shows, when pages are slow, especially on mobile, we don’t react well.
Looks like Google is starting to label sites as “slow” in search results, just like they have been labeling “mobile-friendly” sites when searching from a mobile device for a while now. Web developers, like app developers, should focus on performance. Form follows function. A pretty site that is slow is no longer pretty to the user.