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.
The key to this position is to realize that there is no rush to play a bingo. In this position your immediate bingo chances are quite bleak, but your long term bingo chances are quite good. This is the key to understanding this position. By looking ahead at your opponent’s likely responses, plays like DYER become clearer.