The majority of web hosting services provision many many more (often thousands more) websites than their server hardware can realistically handle. They get away with it because most sites are pretty quiet most of the time; But what this means is at peak times your site is going to slow down, and your customers are going to give up and go elsewhere.
Our hosting server is massively UNDER provisioned, meaning every visitor to your website gets to it quickly without delay. In fact, the normal load average on our server is just 2% !