An IP address is a unique number that separates an Internet site or a web server on the Internet, so in the event that you have a dedicated IP, it'll be used exclusively by your sites and shall not be shared with others as it happens with shared website hosting accounts. If you have your own web server, you shall have a dedicated IP, but you may require additional ones for a variety of purposes. Provided you have a web-based store, for instance, you'll need an SSL certificate for it, in order to make sure that the payment information 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 should 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 may affect its position in search engine results.