Just as there is a warning when editing dashboards that are embedded externally, there should be a warning when editing cards that appear on multiple dashboards. Ideally it would say "You are editing a card that exists across x pages" then the x is a link you can hover and a popup there would show all the pages it is on.
I usually do a decent job of staying on top of this but too often are cards edited on one dashboard without realizing the effects it will have in the context of another dashboard or app. Additionally, the Move/Copy for cards in app studio is basically non-existent unless you go into the card details page and look there.
A warning such as this would reduce most of these errors to nil and prompt the decision to "Save As" a copy of the card first before making edits and losing the history for that card creating much more work.
