1) When you're not using a filter (safety) or 2) Shooting with bright light sources within the 180 degree field in front of the camera sensor (includes the sun) or 3) because you can't take it off. (a la Nikon's 14-24, Canon's 14)
yup, me too. instant protection and a way to cut down undesired stray light (flare)... i can think of no really good reasons to not use one.
I like to leave mine on all the time as well. Even with a UV filter on the lens for protection the hood provides added protection against accidents. With the hood on I don't have to worry about scratching the filter.
I just got this hood today and took a few pictures just to check it out. My inside pictures have a dark shadow at the bottom as if my big head was in the way. Without the hood, no problem. The closer the object, the darker the shadow. Is this just because I don't have a fancy-schmancy external flash? Example: [attachment=1] [This attachment has been purged. Older attachments are purged from time to time to conserve disk space. Please feel free to repost your image.]
Typically pop-up flashes cause that shadow because like Tim said, they aren't high enough to clear the hood. An external flash would solve this problem because they are all tall enough to clear the hood.
you would also be able to bounce off the ceiling which would get rid of that nasty hot spot right in the middle of the helmet.
