An IP address is a unique number that distinguishes a site or a hosting server on the world-wide web, so if you have a dedicated IP, it will be used solely by your websites and won't be shared with other people as it happens with shared hosting accounts. Provided you have your own web server, you will have a dedicated IP, but you may require extra ones for various purposes. Provided you have a web-based store, for example, you shall need an SSL certificate for it, in order to make certain that the payment info which your customers submit will be encrypted and protected. The same is valid in case you have a login form of some type and you want the usernames and the passwords that visitors input to be protected. The SSL certificate requires a dedicated IP, which should be different from the one that you already have on the server. You may also need an independent IP for an app such as a VoIP server, or if you desire a slightly better efficiency for a particular website, which will affect its position in search engine results.