sometimes I misclicked, and actually wanted to undo the sacrifice.Thats the main thing. But there were a couple if niche cases in the very beginning of each where, if I draw a bad hand,just place a rat to stop the hero for a bit, next round, again a bad hand. and so on. i can sacrifice a rat, clear the board and do something better with the next hand.
basically I wish there was a button to remove a piece, even if it cost me treasure, mana whatever to remove it.