Rocker arm shimming clearance question

I think the valves will turn a little, this helps cut the carbon, i:e if your seat width is uneven, carbon would build either side of the narrow seat, so if the valves turn a little either back and forth as mentioned or round and around, this keeps the seat clean , and as said rotators, also some keepers or collets touch together and allows the valve to turn. Springs have natural frequency and do lots of crazy things at certain rpm s.