I am Big, I am Mike
Yes, this is to meter for exposure. A palm is about one stop brighter than 18% grey...so you would meter off of the palm, then add one stop, then fire away.This is to meter for exposure, correct?
So, in terms a simpleton would understand:
1. Arrange the subject (human) in the pose/composition you want.
2. Have them show you their palm.
3. Set the shutter speed and aperture in a way that indicates a correct exposure.
4. Step back and fire away, using these same settings.
No, this can work anytime. If you are taking a landscape shot, you can meter off of your own hand, add one stop, then take your shot. You are essentially measuring the light, (not the subject) if the exposure is correct for the light, it doesn't matter if it's a person or a landscape etc.I assume this method is only for taking shots of people?
Of course, you (as the photographer) have creative control and can over or underexpose as you see fit. That's why I don't get too caught up in metering...especially with digital. If I want more detail in the shadows, I'll expose for that. If I don't want to blow the highlights, then I'll expose for that.
Normally, I try to 'expose to the right', which is to get the shot as bright as possible but without blowing the highlights. Some cameras, (Canon 40D/50D) for example, have a 'highlight tone priority' which actually set the exposure to do just that.