An IP address is a unique number that distinguishes an Internet site or a 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 won't be shared with others as it happens with shared Internet hosting accounts. If you have your own hosting server, you will have a dedicated IP, but you may require additional ones for different uses. In case you have an online store, for instance, you'll need an SSL certificate for it, to ensure that the payment information which your customers submit shall be encrypted and secure. The same is valid if you have a login form of some sort and you wish the usernames and the passwords which visitors input to be protected. The SSL certificate requires a dedicated IP address, which should be different from the one that you already have on the machine. You could also need an individual IP for an application such as a VoIP server, or if you desire a slightly better performance for a certain website, which shall affect its position in search engine results.