I use my sonar so much that I feel "blind" without one.
I've upgraded several units and have found that big and fancy doesn't necessarily catch more or bigger fish, sometimes it's the opposite.
I upgraded from a Humminbird Wide Optic (2400 watts) to a Hummin Bird 747C (4000 watts) last year.
I do a lot of Drop-Shotting and have found that I catch a fish any shallower than 25' deep while running the 4000 watt unit, I suspect the high powered unit is spooking the fish in shallower water.
I have recently purchased a puck transducer for my trolling motor and will be reinstalling my 2400 watt unit for shallow water fishing.
While the 4000 watt unit is real snazzy with the color screen and high definition, it is pretty much useless in shallow water if it's going to spook the fish.
I caught a lot of fish with my old 2400 watt unit and look forward to using it again!!!