An IP address is a unique number that separates a site or a web server on the world-wide web, so in the event that you have a dedicated IP, it will be used exclusively by your sites and shall not be shared with other individuals as it happens with shared website hosting accounts. In case you have your own server, you'll have a dedicated IP, but you may need additional ones for various uses. If you have an Internet store, for instance, you'll need an SSL certificate for it, in order to ensure that the payment info your clients submit shall be encrypted and secure. The same is valid in case you have a login form of some type and you would like the usernames and the passwords which visitors type in to be secured. The SSL certificate requires a dedicated IP, which has to be different from the one that you already have on the web server. You could also need a separate IP for an app such as a VoIP server, or if you want a slightly better overall performance for a certain site, which will influence its position in search engine results.