An IP address is a unique number which distinguishes an Internet site or a hosting server on the Internet, so if you have a dedicated IP, it shall be employed exclusively by your websites and won't be shared with other people as it happens with shared web hosting accounts. If you have your own hosting server, you shall have a dedicated IP, but you may need additional ones for many different uses. Provided you have an Internet store, for example, you'll need an SSL certificate for it, to make certain that the payment info which your clients submit shall be encrypted and secure. The same is valid if you have a login form of some type and you would like the usernames and the passwords that visitors input to be secured. The SSL certificate requires a dedicated IP, which needs to be different from the one that you already have on the server. You may also need a separate IP for an application such as a VoIP server, or if you need a slightly better efficiency for a certain site, which may influence its position in search engine results.