The edge of the takeoff is only one of several basic aspects of a jump. If you go to -3 for the wrong edge error, then you have to go to -3 for every error which violates a basic aspect of a jump, which is pretty much every error. I view that as excessively harsh, and I think most judges, coaches and competitors feel likewise.
To focus only on the wrong edge error because the edge defines the name of the jump is obsessively pedantic. The skater took off, they rotated three times, they landed. They deserve some amount of credit, and certainly more credit than if they had fallen (which also gets the GoE of -3 you would like to give the wrong edge error).
As for your question about how often the wrong edge reduction in GoE is taken -- based on the competitions I have judged this season and the protocols I have looked at I would say with little exception every time the Technical panel has called it. And sometimes even when the Technical Panel hasn't called it.
(And it's a slippery slope when the ice isn't flat.)
LOL...ice is slippery. However, I guess we'll have to agree to disagree. I don't see the point in rewarding a skater any points for a jump whose hallmark is a specific edge and you feel they should get some credit for doing a portion of the jump - so, we'll disagree.

