An IP address is a unique number which separates an Internet site or a web server on the Internet, so in the event that you have a dedicated IP, it shall be employed exclusively by your websites and will not be shared with other people as it happens with shared web hosting accounts. In case you have your own hosting server, you'll have a dedicated IP, but you may need extra ones for a variety of uses. Provided you have an Internet store, for example, you shall need an SSL certificate for it, in order to make certain that the payment info which your clients submit will be encrypted and safe. The same is valid if you have a login form of some sort and you would like the usernames and the passwords that visitors enter 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 web server. You might also need a separate IP for an app such as a VoIP server, or if you need a slightly better overall performance for a given site, which will affect its position in search engine results.