An IP address is a unique number that separates a site or a hosting server on the Internet, so if you have a dedicated IP, it shall be employed solely by your sites and shall not be shared with others as it happens with shared hosting accounts. In case you have your own web server, you'll have a dedicated IP, but you may require additional ones for different uses. In case you have an online store, for example, you'll need an SSL certificate for it, to ensure that the payment info which your clients submit shall be encrypted and protected. The same is valid if you have a login form of some sort and you want 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 that you already have on the web server. You could also need an individual IP for an app such as a VoIP server, or if you would like a slightly better overall performance for a certain site, which may influence its position in search engine results.