I asked my long armer about not using interfacing. She said it plays havoc with the needle. The fabric wants to come up with the needle and it makes a mess. She said she will not quilt a t-shirt quilt without interfacing. You might aqsk your long armer how she feels. Maybe if you are using your domestic machine or hand tying you could get away with it. For me, I will go to the effort to stabilize the shirts.