As far as I can see it the beam takes all the pressure from the mast. The dolphin striker keeps the beam bowing up helping it resist the pressure.

In other words mast press ball, ball press metal rod, metal rod press upper bolt, which push the topside of the beam. The compression tube transfers some of that pressure to the bottom of the beam, without it only the topside of the beam hold all the mast pressure.

It also works the other way. When you install the rod and put some prebend by turning the 3.5 turns if you don't have a compression tube all the pressure is on the bottom of the beam. With a compression tube, the pressure is equalized between the top and the bottom.

I would not install a dolphin stricker rod without a compression tube.