Tom said:
I was recently at an outdoor canine event here in sunny CA, and noticed a pro photographer had a funny-looking 'tent' thingie over the flash. I guessed it was some sort of diffuser, but wasn't sure why she needed it outdoors. Came home and did a little research, and learned she was probably using flash fill to minimize shadows, and the diffuser softens the sharp light from the flash. I've since ordered a diffuser for my flash, and I'm eager to experiment with it.
Yep, the goal is generally to simulate the largest possible light source, from the most flattering direction, giving the softest result for lighting and most closely approximating natural light - the sun through the clouds is a pretty large light source
The worst way to use flash is having one on your camera pointed directly at the subject (like using a built in flash of any kind). When this is the only option, you'll generally want to dial down the flash power so it's not so obvious you used flash.
Slightly better is using one of those diffusers you saw - there are lots of different kinds, none is overwhelmingly better than any others.
Even better is using bounce flash if you have a decent surface to bounce off of (easier indoors), which simulates getting the flash in a different location - turning walls or ceilings or pieces of paper or such into the light source by bouncing the flash off of them.
This is why you see real pros, if they use flash at all, using flashes completely separated from their cameras, and usually fired through umbrellas or softboxes. Those accessories simply make the light source appear larger, and by separating the flash and camera you can choose where your light is coming from.
It's actually not that hard or expensive necessarily - many cheap used older flashes are available that have a 'slave' mode that will fire the flash if they see another flash. So you can turn your on camera flash way down, not affecting the picture much if at all, but still triggering the off camera flash(es) when it fires.
I actually use radio triggers combined with slave triggers, but that's another step up in expense and complication.
In real estate, I've used up to 5 flashes in a single shot like this to evenly light all areas of the property that are shown in the shot, and still balance with the light coming through the windows.
There's a marvellous website out there if anyone really wants to learn about flash use - with free tutorials http://strobist.blogspot.com/2006/03/lighting-101.html
Here are two examples - a simple sunset snapshot with fill flash, flash mounted on the camera and power turned down a bit so as not to bleach out subject. Second one is an off camera flash fired through an umbrella to soften. These are junky low res versions for the forum, but you can probably still see the difference in the lighting, the first is obvious flash, the second should not be: