What effect does shaft stiffness have on a putter?

Thanks for your response Jim. I did shorten my Odyesse putter 2.5 inches from the tip end. If I had shortened from the butt end the grip would not have fit at the bottom. Used lead tape to bring the swing weight up to a DO Have tried it out and seems to work well. Haven’t noticed any difference in the stiffness. Your responses have been very helpful thank.