Same colour occupancy
Although it may limit the power of each piece various combinations of same colour dual occupancy can be very effective. The diagram shows white with a rook and a bishop in the d8/9 field commanding 34 squares.
Note how each piece restricts the movement of the other resulting in a net loss of square coverage for white. However, it also illustrates how the bishop and the rook are protecting each other. The rook is on the bishops diagonal and the bishop is on the rooks d-file.