Each time someone visits your website you have a chance to hook them, and land a customer for life. Every time a customer abandons your website you are leaving money on the table. Long load times are the #1 reason people abandon a website after clicking a link. Google demonstrated this with a massive study of over 90,000 websites. Their main takeaway:
Speed equals Revenue
One of the main concepts Google was looking at was the bounce rate. Meaning the percent of people who click a link to a website and then leave almost immediately.
Increase in bounce rate when page load time increases from 1 second to:
Data from Google's analysis of 90,000+ websites
Loading speed is just one factor in how well your website converts clicks into sales, but it's one you need to have in mind at every stage of building. A beautiful website with amazing copy means nothing if half your potential customers leave before it even loads.