Short answer is never. Assuming you are playing 5 card majors, you have found your 9 card fit. You could agree that 3m shows this hand type. As mentioned any hand with 11 hcp, 4 card support and a 5 card suit is a 7 loser hand or better and you want to force to game. You can use splinter or Jacoby as appropriate Most people will expect only 3 card support when partner starts off with 2m and then supports partner, which may result in missed slams