An IP address is a unique number which distinguishes a site or a web server on the Internet, so in the event that you have a dedicated IP, it shall be used just by your sites and shall not be shared with others as it happens with shared website hosting accounts. In case you have your own server, you'll have a dedicated IP, but you may need extra ones for many different uses. If you have an online store, for instance, you shall need an SSL certificate for it, so as to make certain that the payment info which your clients submit shall be encrypted and safe. The same is valid in case you have a login form of some kind and you would like the usernames and the passwords that visitors type in to be secured. The SSL certificate requires a dedicated IP, which needs to be different from the one which you already have on the web server. You might also need an individual IP for an app such as a VoIP server, or if you want a slightly better overall performance for a certain website, which will affect its position in search engine results.