In this position, REF is a bad setup, since it is easy to block. Plays with the D/G would score well and block the (T)REF setup. However, the concept is solid: you want to create an unblockable bingo line. By playing DYER this turn, you allow yourself to play REF next turn so that your opponent will no longer be able to prevent your setup. DYER is a play that protects your setup; it is a tactical play that blocks any potential block to your REF setup next turn.