Bingo Duane
On valves. The valve is held onto spring with the locks and retainers making it part of the assembly as a whole.
The weight of the parts must be controlled to prevent them from doing what you don’t want them to do. You must consider all the parts as 1 part and all of its weight combined as 1 part.
The spring controls the valve & It’s combined weight with the retainer and lock.
In this scenario for an example, let’s say you have to dumb bells. The small on is 5 lbs. pick it up and hold it over your head, arm fully extended, then shake it back and forth. As fast as you can within a total swing area of 1 foot fore and aft.
Now try I again with 50lbs.
Same idea with the valve, retainer and locks.
To answer the OP’s question, I’ll start be saying, “Good question!” I’ll take a stab at it by saying, once you see/discover a short coming.
OK, that was easier to say than discovered.
I’ll take a second stab at it and suggest a lighter valve would be good or just better if your building a very hot street machine or bracket racer that see action every weekend.
This would help in the longevity of the spring and help in a quicker reving engine.
What exactly are you building this engine for?
Is the cost worth it to you?