I've set the default on my camera to spot metering. Are there times when it should be set to something else?
Rarely would you use spot metering, Tom -- unless you want the metering to be confined to the area of the spot. For example when zoomed in on a bird or plane in flight. Otherwise you want to have the meter consider the reflective light from the entire area of your image. Usually, you would also want that to be weighted more to the center if that is where the subject of the image is located. If you leave it on Spot metering, the portions of your image outside of the spot will not be considered -- and that could lead to a very high or low contrast shot. So the image itself determines the type of metering.
Edit: BTW, am not disagreeing with Ron as to fog/snow metering. In that case, I would want to meter just where the fog or snow is, vs. having other reflected light in the image affecting the reading -- so the spot would be good for that situation as well.
The spot can also be used to view different parts of an image as to the amount of reflective light in each. For example, if doing a sunset, I shoot in manual mode -- and use the spot meter to let me know the contrast between the sun and the surrounding image. An "average" is not much help in that case. Ansel Adam's did most all of his metering with a one degree spot meter. He would look at the highest and lowest amount of reflective light in an image as it applied to the subject of his image to figure what he wanted for an f-Stop and Shutter speed. Digital's do most all of that for us now - or allow us to go back to the basics in manual mode and do it as Ansel did.
