Research shows that the amount of time a user will wait before losing focus is roughly from 0.3 to 3 seconds. If your website takes longer than that to display important information, the user will lose focus and possibly close the browser window.
Websites that are faster will have lower bounce rates, higher conversion rates, higher ranking in organic search, and, of course, they will have an overall better user experience. The bottom line is that slow websites will cost you money and will hurt your brand. On the other hand, making your web pages load faster will positively impact traffic, user retention, and sales.