An IP address is a unique number which separates a site or a web server on the Internet, so if you have a dedicated IP, it'll be used exclusively by your Internet sites and will not be shared with other individuals as it happens with shared hosting accounts. Provided you have your own hosting server, you'll have a dedicated IP, but you may need additional ones for different purposes. Provided you have an online store, for instance, you'll need an SSL certificate for it, to make sure that the payment information that your clients submit shall be encrypted and protected. The same is valid if you have a login form of some kind and you want the usernames and the passwords which visitors type in to be protected. The SSL certificate requires a dedicated IP address, which needs to be different from the one which you already have on the machine. You might also need an individual IP for an application such as a VoIP server, or if you want a slightly better functionality for a certain Internet site, which may influence its position in search engine results.