Not trying to ruffle any feathers, but I am 40 years old, and have been using WD-40 for catfishing since I was a teenager. I can assure you with 100 percent certainty that is WORKS GREAT! There is no if ands or buts about it. If you say it doesn’t work or that it is just a myth, then you have never tried it.
My cut baits and live baits sprayed with WD-40 consistently out fish other baits not laced with WD-40. I’ve tested it many times over the years with people who didn’t believe it, until they experienced it first hand.
One of easy way to prove this is to buy 2 tubs of dip bait for catfishing. In one tub of dip bait spray WD-40 into it full stream for 5-6 seconds and then stir it up and then thicken the dip bait back up with flour. Leave the other tub of dip bait just as it is. Fish with the 2 side by side for a couple outings. See which one catches the most fish. Then you will see.
I have never tried it for any other species personally, but do know people that have used it for bass fishing and claim that it works well.
And yes it obviously leaves a tiny little bit of chemical in the water, but not even close to as much as a boat motor or jet ski does, and people don’t think twice about that.