All devices on the World Wide Web are recognized by a special number called an IP address, for example 220.127.116.11. When you have a site, the domain that you type to open it is for your convenience, however the server where your site files are still has an IP. As there are many more websites and devices than there are IPs, all of the shared hosting servers have a number of sites under the very same IP, whereas when you use a dedicated server you will have a dedicated IP too. Even in the first case though, you will be able to get a dedicated IP for your sites and host them on a shared server. One advantage would be that you may have improved search engine positions since a dedicated IP usually means a faster loading site. Furthermore, you need such an IP in case you plan to acquire an SSL certificate for your website and shield the information that your visitors submit on it.