I hope this makes sense to anyone looking but if not heres another example. (based on a real problem that I had when building decks on here)
I own a Tribal Elf Deck. That deck contains 4 Llanowar Elves, 4 Elvish Champion, 4 elvish Archdruids etc.
Some time after I get board (which happens after playing the same deck for a while) and build a new Elf Token Deck.
I take the 4 Llanowar Elves, 4 Elvish Champion, 4 elvish Archdruids and take them from the tribal deck and put them token deck and know is where deckbox is no longer helpful to me.
As the Tribal deck is listed as having all 4 copies I own in it, the token lists I need to buy 4 of them which is no good because it defeats the purpose of trying to manage my collection on here, and I dont want to delete them from Tribal deck in case I want to rebuild it later or see what it had in it or show someone. So either I can only have currently constructed decks and delete them when Im done, which defeats the point of building on here, or I get to keep all my builds but then my collection information is all wrong which defeats the point of managing my collection on here.
If I were able to set the "in deck" to 0, then on the inventory screen it would show I own 4 and 0 are in a deck, so I know to look in my collection. Alternatively if I then build the Tribal deck It would show I own 4 and 4 are in a deck, so I know there in use. I then build a new Token Deck which has the same cards I go back to the Tribal deck and set the count to 0 and the Token count to 4 so the inventory correctly shows that I own 4 and 4 are in a deck and it dosent tell me im 4 short