I think this should work for any Linux operating system using Gnome, I have tested on Debian and Ubuntu.
Well, automatic login will let you avoid to enter your login and password each time you turn on your PC, this could be insecure, but if your computer is physically secured it is Ok to enable this, that could make your booting more smooth.
How to do it?
On Gnome go to:
Systems->Administration->Login Window, you will be prompted for the administrator password, enter it and then select Security tab, once in there select Enable automatic login and select the user you want to be automatically logged in, each time you turn on your PC.