The main reason to use separation crown is to separate antennas from each other accordingly to producer specifications. Antennas have backward radiation that may lead to interference and high noise bed. Because electromagnetic radiation force decreases with the square of the distance, even small separation is sufficient to improve the situation.
Second task of a separation crown is increasing the mast torsional stiffness (with additional set of guy wires). Truss masts are quite robust for vertical forces (inherit feature of a truss), average for horizontal forces (thanks to guy wires), and relatively non resistant for torsional forces (hence idea to help here). Twisting is most problematic during high winds and service jobs. This is especially problematic for radiolink, because it may interfere with or even break connection.