Second Life is a 3D virtual world. Those of us who can, go out or online and spend what we can afford on graphics cards that will display SL as we would like. We all read the reviews and press our faces against the virtual windows of the storefronts with the cards we can't afford.
So why do some think the ideal SL photograph obliterates SL's 3Dness?
I posted about it when I first came across it. Alas, the excellent Ophelia Drowns is now invitation-only,. so you may not be able to see the images in the "Picture Perfect" post there... but you can see "GoGo's Lighting Tips" on the Juicy Bomb fashion blog. The goal: a photo that utterly flattens the image. The model looks like a dress-up paper doll in some Dover Press collection, without the hard-edged style.
Ah, but those posts are from years ago. Perhaps their authors' opinions have changed... but we've read Mariko Nightfire's more recent two posts (so far) on the desirability, or undesirability, of what she calls "walking with windlight" (a phrase that makes me hear Patsy Cline in my head).
If you look at the photos in the later post, again the photos labeled as better are flatter. I think that's partly because the skin, the face especially, has shading painted on, so that ironically, flat lighting makes the fake shading look better, though it also enhances the effect Galatea Gynoid points out in a comment in NWN: it looks like her head was Photoshopped into a flat drawing of the rest of her. (Not having "real" shadows causes that effect. If her head were really there, it would cast a shadow on her neck, and even if you can't point that out, it sets your mental teeth on edge. Alas, years after it first appeared, shadows are still not officially supported in LL's client, so that's LL's fault.)
Windlight gives us directional sunlight and moonlight like RL, rather than the uniform lighting of pre-windlight SL. Harsh shadows in RL don't distract you, any more than someone standing between you and a tree does. (After all, you're keeping an eye out for predators... or rather, your ancestors were.) Take a picture of it, though, and they're all you see. "Darn, those shadows are harsh. Oh... What's growing out of Billy's head? BWAHAHAHA...."
That's why photographers schlep flash and reflectors, and why photographers in SL keep transparent light sources in their inventories. I use a facelight, but only as fill lighting, and I do my best to take it off when I no longer need it. It's dim, and easy to forget.
So, is the Second Life client window more like RL, or a photograph? In a NWN comment, I claimed it was like the photograph, but I think I've changed my mind. I will never do without windlight unless I'm on a computer that can't support it, and the only times I recall lighting or shadows being a distraction are in stores so brightly lit that everything is washed out, or where someone steals the beacon from a lighthouse and points it at herself. (It's always herself, in my experience.)
So, like the vast majority of things in SL, it's up to you, the hardware you have available, your SL client, and what you want. I can't count on a "shared experience" with whoever's there, as far as the environment goes--who knows what they're running, or what their environment settings are? The sky and water's appearance and how I can use their effect on my surroundings are more important to me. Your mileage may vary.
P.S. Juicy Bomb is well worth reading... the author covers some really nice clothing, hair, and shoes.