I have never had much luck "seeing" fish on the finder. I use mine for checking out the bottom trends, structure and compsition. So I use the 20hz single. In 20' of water, the cone is like 3' in dia. Not a very big picture, but if I want to see the fish, I could probably just look over the side. I usually fish in water under 30' deep.
If I were jigging to fish suspended off the bottom, a fish finder could be a handy spotting tool. I am usually casting to structure that I can't motor over. Lately I have been turning the finger off if I am fishing in an especially "quiet" or pressured spot. I wonder if the fish can feel the pulses and associate that with a threat. Probably doesn't make any difference.
How do others use their fishfinders?
One cast can change your day...maybe your life.