An IP address is a unique number which distinguishes a site or a server on the Internet, so in the event that you have a dedicated IP, it shall be used exclusively by your Internet sites and won't be shared with other people as it happens with shared web hosting accounts. If you have your own web server, you shall have a dedicated IP, but you may require extra ones for a variety of uses. In case you have an electronic store, for example, you'll need an SSL certificate for it, in order to make certain that the payment information which your clients submit will be encrypted and safe. The same is valid if you have a login form of some sort and you would like the usernames and the passwords that visitors enter to be protected. The SSL certificate requires a dedicated IP, which should be different from the one which you already have on the server. You could also need an independent IP for an app such as a VoIP server, or if you need a slightly better efficiency for a particular website, which may affect its position in search engine results.