An IP address is a unique number which distinguishes an Internet site or a server on the world-wide web, so if you have a dedicated IP, it shall be used only by your websites and won't be shared with other individuals as it happens with shared website hosting accounts. If you have your own server, you'll have a dedicated IP, but you may need extra ones for different purposes. Provided you have an electronic store, for instance, you shall need an SSL certificate for it, in order to make certain that the payment information which your clients submit shall be encrypted and safe. The same is valid in case you have a login form of some sort and you wish the usernames and the passwords that visitors enter to be protected. The SSL certificate requires a dedicated IP, which ought to be different from the one that you already have on the machine. You may also need an individual IP for an app such as a VoIP server, or if you desire a slightly better efficiency for a certain site, which shall influence its position in search engine results.