The spheres are not the "shock absorbers". The spheres are springs, just like the coil springs; they work together. They also "store" SLS fluid so that the valving inside the struts can control the compression and rebound. If you compress a strut with a bump, the piston is forced upwards. But the only way it can move upwards through the SLS fluid is to "wait" for fluid to be forced through the valving. (I have no idea what valving is used, but it doesn't matter for this discussion, although it does for the OP's question) This is what dampens bumps and stops the car from pogoing up and down after a bump. Now, since the piston is going up, and the volume of the strut above the piston is greater than below, (because of the volume of oil the piston rod displaces) that extra fluid has to go somewhere. If the leveling valve is closed, it can only go to the sphere. If the leveling valve is open, it can go to the reservoir (lower mode) or to the sphere (raise mode). This serves to increase resistance to the upward movement, stop it, then force the piston back down through (probably) a different set of valves to get back to a position of equilibrium.
The function of the strut most closely resembles a conventional shock absorber, the difference being that a conventional shock absorber is not completely full of oil. This is to allow for the different volumes of displacement on one side of the piston vs the other. (And in the last 30 years, a gas charge) Of course, the strut also plays a role in ride height, unlike a conventional shock absorber.