What You Need: A controlled environment. It doesn't work very well to be shooting tethered on the move, because then you'd be moving your camera and your laptop, external hard drirves, possibly even lights. Being attached to your computer can take out a little bit of the spontaneity of photographing something, but in some instances, it's perfect.
How it Works: When you buy any of the newer DSLRs, within your camera body package should be a small cord that attaches from the camera body to the computer. If you plug in your camera to your computer, the software to run it may already be installed there to run it. If not, it will have come with a disc to install on your computer. All the programs are pretty intuitive to shoot in this fashion, just click and see the images appear! Look Out For: Slowing Down the Shoot. This can slow things down, shooting afixed to the computer. There's a slight lag time between triggering the shutter and the image downloading onto your computer to view. So if you're shooting people, especially kids, you'll lose all the magic and slight change of expression so important in getting that job done. Also, fussing too much with each shot can bog you down, be decisive, be bold and keep moving.
Getting the shot right with "Live View" part of capturing the imag.What It's Perfect For: A big product, still life or food shoot. You can use a similar set up and backgrounds and just position your computer and your camera on a tripod and get through a lot of photographs! Being able to "Live Capture" which is literally seeing what your final frame is as you compose it can save hours in post production and general frustration. Always nice to get things right in camera, and this allows you to do so. Do you ever shoot tethered? How does it help or affect your process? Do share.
The final shot of my Holiday shoot, which I did entirely tethered.(Images: Leela Cyd Ross, image of tethered camera/computer by mkeefe licensed under the Flickr Creative Commons)