It's a no-brainer: well performing websites enjoy higher visitor engagement, retention and conversion.
Increasing Website Performance
The performance of websites and the impact that has, has been well documented over the years. In 2007 Amazon reported that for every 100 ms increase in load time of Amazon.com their sales decreased by 1%. Google also reported similar results in 2006 with their Google Maps product. Google found that by reducing the size of the page from 100KB to 80KB, their traffic shot up by 10% in the first week and then 25% in the following three weeks.
It’s clear that monitoring the performance of a website is a must and should not be ignored as being an integral part of your web design workflow.
Via Brian Yanish - MarketingHits.com