Assume that you are under the auspices of a RA that allows the question:
No [suits] partner?
Declarer, intent on ruffing a side suit in dummy, plays a winner which partner ruffs.
Partner later turns up with another card in that suit.
You could have asked partner if they were void when they ruffed, but you didn't.
Do you bear any responsibility for saving partner from their revoke?
Anyone can missort their hand, no?
Or have a card hidden?
Benefits include:
Plus... it's free!