Consequences of poor site performance
If your site has poor performance, your visitors or your analytics will let you know. Without an indication that a web page is loading within a few seconds, a visitor will "bounce" to a different page. Visitors may message you directly, or complain about slow response times on social media.
The following image, taken from Find out how you stack up to new industry benchmarks for mobile page speed, shows how quickly the bounce rate climbs as page load times increase.
Page bounce probabilities
The conclusion is clear: if you want to keep visitors engaged, you need to keep your load times to a minimum.