But what part of the histogram would you be looking at that would tell you the correct exposure? I’ll give you and example. Same light, same spot, but with two different subjects. One subject has very pale skin wearing a white dress, I get the correct exposure using an incident meter and take the shot with her dominating the frame. I then shoot a dark skinned guy with a very dark suit and take the shot. I’ve already metered using the incident meter – remember the light hasn’t changed. If you looked at the histograms, they would be wildly different – the white dress would be pushing the right side of the histogram(overexposure according to the camera meter), the dark suit would be very close to the left side(underexposure according the camera meter) – completely different, yet they are both properly exposed. All the histogram has told you is the range of tones in the photo, not whether those particular tones are accurate. Again, think if you couldn’t check your LCD and all you had was the camera’s meter, how would you determine your exposures?
Again, I’m probably sounding like a jerk but the OP made a good point – all the modes can have their uses, and telling people to use nothing but manual mode can be a false sense of control. It’s just as easy to use EV comp as it is to flip to manual and under/over expose according to the meter. And you can also use AE_L to “lock” in the exposure in any of the more advanced auto modes (aperture, shutter, and program).
In the end, use whatever works – I’m no different in that I “chimp” exposures but that’s because I’ve been shooting for a while and have a pretty good feel. Exposure is also part of the creative process. But for a beginner I think it’s important for them to know why and when to use manual. And that begins by understanding why the meter reads a certain way, why it fails, predict when it will fail and be able to fix it.
Stepping down from soapbox…..