All devices on the World Wide Web are recognized by a unique number called an IP address, for example 220.127.116.11. When you have a site, the domain that you type in order to open it is to save you time, but the server where the website files are still has an IP address. As there're a lot more websites and devices than there're IP addresses, all the shared web hosting servers have a number of sites under the same IP, whereas when you use a dedicated server you'll be given a dedicated IP too. Even in the first case though, you'll be able to obtain a dedicated IP for your websites and host them on a shared server. One benefit would be that you'll get improved search engine positions since a dedicated IP often means a faster loading site. Furthermore, you need such an IP when you want to get an SSL certificate for your site and protect the information that visitors submit on it.