if i tie a quilt, i do it so the threads dangle on the back, usually 2" or 3" apart. if you use a color thread that coordinates with the front but contrasts with the back, it doubles as decoration on the back.
you can also "tie" a quilt in a way that leaves nothing dangling from the back. instead of tying knots, do several backstitches (like you were sewing on a button), run your needle through the innards, then bring it back up at the next spot to "tie".