Indeed. I compiled a list of how this could be useful into the notes, but it'll probably be more visible here:
"Benefit of being able to add New tags to cards and immediately play them, being able to hide revealed cards without playing or discarding, foiling opponent's cards that affect "matching non-Rare" in their effects, moving Horde cards together, and staying on hand."
One other side effect I only just now considered is that this would make the achievements for playing X number of Rare cards easier to gain. Wasn't considering that. Someone who has a card to end the match could play this several times first just to inflate that total. Seems unfair to me.