Reading the other posts here gave me some time to think. It certainly wn't hurt anything to back the weight down, even below the minimum. I don't think this would help the limbs as much as it would the string/cable. These would probably creep over time so relieving stress on them would most likely keep them from creeping.
I shoot my bows regularly so don't drop the weight down. The longest I ever had a bow was 10 years and never backed that one down and it lost only about 2# of draw weight over the years. Now whether this was due to the limbs losing strength or the string creeping I could not say. This was way back when all we had was wood/glass laminated limbs and steel cables. It was long before such technical things came to light and as I said, I shot my bows almost daily.