If the dampers impair the tube's ability to get rid of heat then you can expect a shortened service life out of the tube. But usually they are a good thing sonically.
I have heard people say that there is a problem with loss of air due to the tubes being overdamped. Such a thing is not actually possible, FWIW.
I have heard people say that there is a problem with loss of air due to the tubes being overdamped. Such a thing is not actually possible, FWIW.