An IP address is a unique number that identifies an Internet site or a server on the world-wide web, so in the event that you have a dedicated IP, it'll be used only by your sites and won't 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 extra ones for a variety of uses. If you have an online store, for instance, you will need an SSL certificate for it, in order to make sure that the payment information your clients submit shall be encrypted and safe. The same is valid in case you have a login form of some kind and you want the usernames and the passwords which visitors input to be protected. The SSL certificate requires a dedicated IP address, which ought to be different from the one that you already have on the hosting server. You could also need an independent IP for an application such as a VoIP server, or if you would like a slightly better overall performance for a particular website, which shall affect its position in search engine results.