Guest user account for people who do not have individual accounts, this account can do no harm to your computer because the user profile will reset once machine restarted. So if you are having any public machine which has internet connection and want to allow all of them to access the machine, that time you can allow them to login as guest. But they could see the list of account names; might be a chance to ask you to create account for them, it is better to login automatically with guest account. Here is the small tutorial about enabling guest auto login in Linux Mint 12.
Step 1: Open Terminal ( Applications —–> Accessories ——> Terminal or Ctrl + Alt + T)
Step 2: Edit the following file.
raj@geeksite~/$ sudo gedit /etc/lightdm/lightdm.conf
Step 3: Add the following line at the bottom of the file.
allow-guest=true autologin-guest=true autologin-session=lightdm-autologin autologin-user-timeout=0
Step 4: Reboot your machine.
raj@geeksite~/$ sudo reboot
That’s All. Now the Linux Mint will not show any login screen, it will automatically login with Guest Account.