Arj,
I use the weight over the speakers for vibration control. I had a lot of extras from my previous system and am trying to use them up. The weights and isolation on the subwoofer do alot though and really improve bass making it both tight and musical. I think the weights on the speakers make a slight improvement, but that one could just be placebo. I've been trying a lot of new stuff on my recordplayer, so I haven't had time to retest. As soon as I do, I will let you know more.