No one likes slow websites and often, people leave if loading takes too long. Think about how much frustration you experience when Facebook is slow.
Of course, the upside to this fact is great. Because increasing your website loading speed can prevent that loss of 7% in possible conversions. You can do this by optimizing certain elements on your pages.
The quicker people can access your content, the more likely they are to take a look around. Which leads to more customers in the end.