I often see Internet discussions where a newcomer to the world of photography posts a question about which mode to use when photographing a specific subject, and invariably there will be someone who claims that one should only shoot in Manual mode because that's the way the pros do it. After all, you upgraded to a DSLR so you can better control the camera—not so you can let the camera do all the work, right?
The fact is, most professional photographers use some form of automatic settings for the majority of their work. The two most common exposure modes are Shutter Priority, also called Time Value (Tv), and Aperture Priority, or Aperture Value (Av). In the truest sense, these two exposure modes are semiautomatic, since they require the photographer to control at least one aspect of the exposure settings. If everyone bought DSLRs so they could manually control every aspect of focus and exposure, then the manufacturers wouldn't spend millions of dollars of research designing and improving upon things like metering and autofocus because it would all be done in the photographer's head.
Almost no photographer looks at a scene and intuitively knows the exact exposure. You can use the "Sunny 16 Rule" as a jumping-off point, but every scene is different and must be taken as such.
Most photographers who shoot Manual exposure use the camera's built-in light meter, the same light meter that the camera uses when determining settings in automatic exposure modes. The photographer is using his or her brain to decide which combination of shutter speed, aperture and ISO will get the image created expressively, but he or she still is relying on the camera's ability to accurately measure light for the actual exposure.
What if you could choose your settings for creative purposes, but allow the camera to do most of the work when it came to adjusting for those settings? The good news is that, with most DSLRs, you can!
First and foremost, I'm not recommending using the fully automatic point-and-shoot mode that most cameras have, often referred to as the "green" mode because of the icon that commonly denotes it. I'm also not recommending the little brother to the green camera mode: the fully auto flash-off mode. These modes don't allow the photographer any creative flexibility at all.
The key to making automated settings useful is to take control of them by knowing how they function and by setting parameters for them to work within. When you know what the camera is doing and why, the automatic settings aren't so unpredictable after all.