Initially the cam moves the valve, but after it starts moving you need spring to control the inertia and control bounce. Lighter valves
Have less inertia, kinda like lighter weight pistons are easier on your rods and bolts.
I get it.....I guess what I should have said was, IMO it's splittin the HELL out of hairs to take a chance on using hollow valves. Valves crack and break sometimes as it is. Yall use that ****. I'm stickin with with solid ones.