Auto has always and continues to receive a lot of bad press but it's high time Manual got the same treatment. Manual is not the end all be all of great photography. Here's what you need to know. When you are shooting in manual mode you must decide on an f/stop; one could argue this is one of the key reason why photographers choose to shoot in Manual. However the usual reason for moving f/stop is not only to control volume of light but also to control depth of field; unfortunately most of the time, depth of field does not move as quickly as photographers believe it is. See images below.
Unless there is significant amount of relative distance between the subject and the camera and the subject and the background, like below, OR you are in very close proximity to the main subject, moving your f/stop will not make much of a difference at all.
But if you could and want to control the depth of field, you still do not need to shoot in Manual. You could use Aperture Priority. If you were to shoot in an Aperture Priority mode your camera would then optimize your shutter speed based on the focal length of your lens. There is an optimal shutter speed you ask? Yes your camera knows which focal length you are using and is now calculating for the optimal shutter speed for a hand held exposure! If you are using manual mode and you are NOT shifting your shutter speed per your focal length, there is a strong probability that you are going to have problems with your photographs.
The second reason to shoot in manual is to control the shutter speed. The reason for controlling shutter speed is usually related to photographing moving objects or to create a special affect. If you are a sports photographer you are likely trying to stop action and therefore need a faster shutter speed. But why shoot manually? Why not shoot in Shutter Priority? Although there are reasons, they are few and far between; one of those reasons is to control exposure but exposure can be much more easily controlled with exposure compensation in Shutter Priority than Manual mode. Also, when using Shutter Priority the camera will choose an optimal Aperture (f/stop) for the sharpest image the lens is capable of rendering. One instance where you would need to use Manual mode instead of Shutter Priority, is when you require an exposure longer than 30 seconds to create a special affect and this is beyond the calculating capabilities of your camera; normally most cameras cannot calculate beyond 30 seconds. The times when you need to have a particular aperture and a shutter speed over 30 seconds is exceedingly rare. As a result when most photographers shoot in Manual mode they are not getting optimal exposures.
If you are photographing something where shutter speed is not important (eg. non moving objects) and where changing your f/stop has little affect or no affect (most instances) why not shoot in an Auto Mode and allow the camera to make an optimal calculation for the sharpest photo possible? If you are using manual mode and are not making all of these calculations every time you press the shutter button you are not optimizing your equipment. This is why manual can suck.