The point of 'gaining root' is more about what it implies: That you're not root, normally. Most Windows users I know end up with letting their login account have Admin rights, because otherwise everything just gets too cumbersome. Which lets them open to every kind of attack there is.

On a Mac the user account and the admin (root) account are separated, and 'system' work is done via 'sudo', which we also have, which allows certain privileged commands to be run by an unprivileged user account.

On Linux the user never logs in as root to do general work. Except that I've heard about newcomers doing this, to begin with, because coming from Windows, they thought that was OK if the computer was a single-user computer. It's not so. Because of this some versions of GUIs on Linux won't even let you log in as root. You have to log in as yourself, and then use sudo or something else from there.

Now, to gain root: On some Linux-based systems, e.g. Android, (and other systems like the OS on the iPhone, as far as I know) root is 'locked out', i.e. not accessible for the owner of the device. Which means that you can only install applications approved by the authorized application manager app., for example. You can only do what the designer set out to allow you to do. On the Maemo devices you are free to 'gain root', if you want to, although you will have to consciously install the necessary software to do so, so that it won't happen just by accident. Having gained root, you can change almost anything on the device, and install whatever you want, and you're also free to render your device utterly useless. The point is that it's your device, so it's your choice. But for normal use you don't have root privileges, so to 'click' on something in a web page can't just damage your system via javascript or something.