An IP address is a unique number which identifies a site or a web server on the Internet, so in the event that you have a dedicated IP, it shall be used exclusively by your Internet sites and shall not be shared with other people as it happens with shared hosting accounts. If you have your own hosting server, you will have a dedicated IP, but you may require additional ones for a variety of purposes. If you have an online store, for instance, you shall need an SSL certificate for it, so as to make sure that the payment info which your clients submit shall be encrypted and secure. The same is valid in case you have a login form of some sort and you want the usernames and the passwords that visitors input to be secured. The SSL certificate requires a dedicated IP address, which needs to 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 desire a slightly better overall performance for a certain website, which may affect its position in search engine results.