Because multiple sites hosted on same IP address it is not possible to access site using IP address alone. Because when you typing IP address alone this request goes to server but server unable to identify which domain you are looking for.

Dedicated IP

Dedicated IP or Static IP address your website specifically assigned for one domain name. So one can access your site by typing dedicated IP address and your site will be open in the browser. You need dedicated IP address if you need SSL, private name server and other service that are not accessible with shared IP address.

Need Dedicated IP Address

If you want to use SSL on your site you must need Dedicated IP address. It can also help to optimize your site for search engine. Because if any site hosted on shared IP address and if it banned by search engine and risk involved of IP ban.