Most of the times weights are used to fine tune your clutch to the rpm range desired. I don’t claim an expert on this but maybe some of the clutch tuners on here can give the science. In a nutshell like a flame clutch: you use springs to get you to a set rpm and then add small weights to the shoes to make them slightly heavier to come in contact with the drum a little sooner. spring changes get you larger jumps and in the ball park while weights are smaller incriminates.
More weight will yield a more positive engagement. You have to accommodate the heavier weights with stiffer springs to get the engagement rpm back to where you want it (peak torque.)
Spring heights are more of a fine adjustment, while weights are gross adjustments in engagement.