When the subject is not aware of the camera (at least, at the moment when the photo is being taken), the resulting candid portrait is often much more alive and “real” than a posed one, although the latter is often better executed from a technical standpoint. Professional models are trained to take the full advantage of a posed photo shoot. They know exactly what poses, view angles, lighting, etc. work best for them and, most importantly, can consistently reproduce their best poses. On the other hand, candid portraits makes “mere mortals” equal to pros in some respect, since it is much easier to be relaxed and behave naturally if one is not aware of the camera. In this case ignorance is, indeed, bliss.
I find that one interesting exception is photographing small children if they genuinely like being photographed. My three-year-old daughter is like that (most of the time). Everything in her world, photography, is a game to her. When she asks me to take a picture of her, she is fully aware of it, but somehow remains completely relaxed and continues whatever she was doing without missing a bit – exactly as she was doing it a moment earlier. I think this is because it all part of playing: she would “pose” for the camera one instant, run over to see the picture on the LCD the next second, and grab a camera to take her own picture of something that entered her attention field the moment after that. Incidentally, just as my daughter does not discriminate between playing model or photographer, the subjects of her photos (taken with an indestructible toy camera) uniformly span the range from portraits of her mom and dad to closeups of parts of furniture and toys to stickers of “Frozen” characters attached to whatever happened to be within reach.
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