What is Full Auto Mode?

Why should anyone bother about the settings, if the camera can do it for you? Exposure, Aperture and Shutter Speed are auto-adjusted to expose the image rightly. You may be intrigued to use this mode when using an SLR for the first time. Works same as a point-shoot camera. Rotate the dial, and the camera sets everything for you.

High contrast situations with a very bright background are not ideal for any cameras. Very bright and dark objects in the same frame is a big no-no for this mode. Exposure will not be right every time, and you will have a difficult time figuring what went wrong.

A portrait is not made in the camera but on either side of it. Edward Steichen

If you ever happen to use an external flash or an in-built one for that matter, you will look like a novice. Flash will be hurling at undesired circumstances and won't fire while needed. The reason for this is because the sensor will have a terrible time differentiating 18% grey in bright scenes with dark areas. Be informed that you will regret the decision to select this mode soon.

On a lighter note, learn to control your camera settings before you get out of control.