There are 2 very important reasons a coin can give a high tone and high ID in one direction, and a low tone / low ID when swept at 90°.
One, the coin is on edge or edged...and most coins in the ground are on edge or edged.
Two, the coin is right beside a low conductor.
Both of those reasons is why you hunt, then hunt again at 90°. In other words, a high ID and tone usually means a high conductor, and it doesn't matter that you only get it in one direction. If you ignore targets that only have a high tone and high ID in one direction, then you're missing a significant amount of coins.
A good cherry picker will leave little behind. Sure, someone else can hunt the site at a later time and might find a coin or two, but that's going to require digging a massive amount of junk. Some might find that acceptable, but I sure the heck don't.
If you take a good cherry picker and more of a "dig all" detectorist and put them in a park like setting for a few hours, then the good cherry picker will walk out with mainly a bagful of coins, and the other will walk out with mainly a bagful of junk.
