Out of many metrics Google users to rank your website, one is page loading speed. In recent years Google has drawn attention to fast loading time on mobile in particular. You can test your website here.
There are two main factors affecting your website's speed:
Your bounce rate is calculated from when a visitor opens your website and then leaves without further interaction.
Page loading speed is a huge factor here. Think about the last time you closed a tab because the website was taking too long to load; we've all done it!
When a visitor discovers your website your aim is to guide them to a call to action (abbreviated to CTA). Whether that is a contact form, newsletter or making a purchase.
A slow website can cause your visitors to leave with frustration if each of these steps takes too long.