An IP address is a unique number that separates a site or a server on the Internet, so in the event that you have a dedicated IP, it'll be used exclusively by your websites and won't be shared with other people as it happens with shared hosting accounts. In case you have your own web server, you shall have a dedicated IP, but you may need extra ones for many different purposes. In case you have a web-based store, for instance, you'll need an SSL certificate for it, to make certain that the payment information which your clients submit shall be encrypted and protected. The same is valid in the event that you have a login form of some type and you wish the usernames and the passwords that visitors type in to be protected. The SSL certificate requires a dedicated IP address, which has to be different from the one that you already have on the server. You might also need a separate IP for an app such as a VoIP server, or if you need a slightly better performance for a given site, which will affect its position in search engine results.