Another harmonic dampener/balancer question

I was planning on using my stock dampener because it looks to be in excellent condition (rubber looks great and it has no mars anywhere) but after reading another post here I see you guys that build engines all the time say you allways replace the dampener. Why do you allways replace it? Is it because you feel the stock one is an inadequete unit or because most of the time the stock one is worn out/rubber is brittle? I see a couple guys recommend the Professional products balancers which can be bought very cheap. I could afford one if it would be a gain. One other thing. I had my assy. balanced using my stock balancer. I don't think it would mess up the balance by swapping to a new balancer but what do you guys think? The engine this is going on is a 360 that will produce approx. 375-400 hp and spin to about 6000 rpm.