Jailbreaking an iPhone and Rooting a linux based system like Android are two completely different processes.

First question we'll tackle is "what is root?":
To have root access on a linux based system such as android means you have the equivalent access of Administrator on a Windows based computer. You will have unrestricted full access to nearly all aspects of the android system stack.

Second question "why would i want to obtain root access on my phone"
For those of us who would like an extreme level of control over our phone's files, root access is a necessity. Having a rooted phone gives the end user unprecedented control over the phone, enabling them to have limitless possibilities. Essentially unlocking your phone's full potential. With root/superuser access on your phone you would be able to flash modified roms (roms from other devices) , have access to certain functions on "root only" applications (example: wireless tether for root users - ability to tether your phone). The possibilities are endless.