can anyone here describe to me what is the advantanges by having full control over our domain name. From what i observed, full control domain is costly..?

I don't know - I thought when I registered a domain I had full control over it. Who do you think controls your domain name? And no, owning your domain name is very cheap, only a few dollars a year, depending on your registrar.

When you register a domain, the registrant info provided will be the owner of the domain.

When you have full control of the domain, you should have some sort of access to modify the domain info and to change things such as the nameservers or other features provided by the registrar. Another way would be the registrar or hosting company itself may manage the domain info etc for you. But you should still be the registrant.