Convenience
In the convenience tab you can configure some options that make life easier for lazy people, like automatic login or disabling passwords.
Important
Please think more than twice before using these options. Every option in the Convenience tab is well-suited to seriously compromise your system security. Practically, these options are only to be used in a completely non-critical environment, e.g. a private computer at home. 
Automatic Login
Automatic login will give anyone access to a certain account on your system without doing any authentication. You can enable it using the option Enable Auto-login.
You can choose the account to be used for automatic login from the list labelled User:.
Password-Less Login
Using this feature, you can allow certain users to login without having to provide their password. Enable this feature using the Enable Password-less logins option.
Below this option you'll see a list of users on the system. Enable password-less login for specific users by checking the checkbox next to the login names. By default, this feature is disabled for all users.
Important
Again, this option should only be used in a safe environment. If you enable it on a rather public system you should take care that only users with heavy access restrictions are granted password-less login, e.g. guest.
You can also choose which user is “preselected” when kdm starts. The default is None, but you can choose Previous to have kdm default to the last successfully logged in user, or you can Specify a particular user to always be selected from the list. You can also have kdm set the focus to the password field, so that when you reach the kdm login screen, you can type the password immediately.
The Automatically login after X server crash option allows you to skip the authentication procedure when your X server accidentally crashed.