It can have a huge impact or it can make you a sucker, find one massive school and you’re a genius. Drive around all day looking for fish and can’t get them to bite, you’re a donor.
I do think a person could waste too much time relying on it for many lakes though. I “think” it would be beneficial on clear canyon types of lakes, not as useful in grass lakes.
We have done very well with it and it has made a huge difference in a few tournaments for us. But, we have invested a bunch of time into learning how to use it. However, for roughly half the tournament we fished, we didn't even turn the graphs on except to navigate using the maps. Like grout-scout said, I would think it would be very benificial on deeper clear lakes. I have been fishing for most of my 57 years on the planet and using it has taught me a lot about bass behavior that I thought I already knew. Going forward, I can't imagine not having it. Pay attention to the leaderboards. It will definately be a player on some lakes. If you can go fish with someone who actually knows how to use it, you will see!