I'm in the depth finders as a tool camp. When I'm fishing the shallows, or the local BV lakes that I know like the back of my hand, I don't even turn them on. I'm also a little suspicious that the constant tick-tick-tick noise the sonar makes, may alert the fish that you are in the area. Or maybe not, I'm still on the fence on that one.
But, if I'm fishing the drop shot, or winter fishing in the depths, or fishing the depths at any time, I use it a lot.