An IP address is a unique number which distinguishes a website or a hosting server on the Internet, so in the event that you have a dedicated IP, it shall be employed just by your sites and shall not 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 need extra ones for a variety of purposes. Provided you have a web-based store, for example, you'll need an SSL certificate for it, in order to make certain 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 type and you would like the usernames and the passwords which visitors enter to be secured. The SSL certificate requires a dedicated IP address, which should be different from the one that you already have on the machine. You might also need an individual IP for an application such as a VoIP server, or if you want a slightly better efficiency for a certain website, which shall affect its position in search engine results.