There are many reasons why a slow website can have a detrimental effect on visitor numbers and ultimate enquiries. The main two are:

  1. If your site takes longer than three seconds to load the bounce rate will increase dramatically.
  2. Google uses site speed as a metric to rank your website so a slow website means lower rankings.

More reasons are details in the below infographic.

How Speed Affects Your Website (Infographic)

Infographic courtesy of hostingtribunal.com.