One of the problems I have with metering, snapping, looking and chimping is I have learned the LCD panel is very unreliable in determining what the exposure actually looks like. Historgrams come to aid a little, but even they change depending on the scene, and as we know, there isn't one "correct" histogram. There are as many different histogrms as their are correctly exposed images.
Perhaps returning to the histogram discussion on a previous thread will answer all my questions.
So...in camera systems are very reliable for 90% of what we shoot. (I was told this by a school photographer...that the in camera system of the Canon 20D he was using was better than his light meter). So the real question of proper exposure is what does the photographer want properly exposed in the image.
In my example stated above for the outdoor portrait, since the faces of the people are most important, metering off of their faces, even doing the lightest, darkets, averaging method, would provide correct exposure. The photographer would just have to accept the under or over exposed background.
That is, of course, unless a fill light were introduced. Then we have the method of metering the background and using fill flash to bring the faces to the same exposure as the background.
Tim Kelly, when doing outdoor portraits, looks for an area with open sky in the shade and a spot where the light coming through the foilage creates a rim light around the subjects. He then meters their faces and shoots. No fill flash or reflectors. I find that somwehat amazing.
My Video Daily - The Outdoor Portrait (Part 1) with Tim Kelly - Free Streaming Video