An IP address is a unique number that distinguishes a website or a web server on the world-wide web, so in the event that you have a dedicated IP, it shall be employed only by your websites and won't be shared with other people as it happens with shared website hosting accounts. If you have your own hosting server, you shall have a dedicated IP, but you may need extra ones for various purposes. If you have an Internet store, for example, you will need an SSL certificate for it, to ensure that the payment info that your customers submit will be encrypted and protected. The same is valid in case you have a login form of some sort and you wish the usernames and the passwords which visitors type in to be protected. The SSL certificate requires a dedicated IP, which should be different from the one that you already have on the server. You may also need an independent IP for an app such as a VoIP server, or if you would like a slightly better functionality for a particular website, which shall affect its position in search engine results.