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'll be employed only by your sites and won't be shared with others as it happens with shared website hosting accounts. If you have your own hosting server, you shall have a dedicated IP, but you may need extra ones for various purposes. In case you have a web-based store, for instance, you shall need an SSL certificate for it, so as to make sure that the payment information that your clients submit shall be encrypted and secure. The same is valid in case you have a login form of some kind and you would like the usernames and the passwords which visitors enter to be protected. The SSL certificate requires a dedicated IP, which needs to be different from the one which you already have on the hosting server. You might also need an independent IP for an application such as a VoIP server, or if you want a slightly better overall performance for a certain site, which may affect its position in search engine results.