An IP address is a unique number which distinguishes a site or a hosting server on the Internet, so in the event that you have a dedicated IP, it shall be employed exclusively by your sites and won't be shared with other individuals as it happens with shared web hosting accounts. If you have your own server, you will have a dedicated IP, but you may need additional ones for a variety of purposes. In case you have an Internet store, for example, you will need an SSL certificate for it, in order to ensure that the payment info your clients submit will be encrypted and secure. The same is valid if you have a login form of some kind and you wish the usernames and the passwords which visitors enter to be secured. The SSL certificate requires a dedicated IP, which ought to be different from the one that you already have on the server. You could also need an individual IP for an application such as a VoIP server, or if you would like a slightly better efficiency for a given site, which will affect its position in search engine results.