the best advice is cost benefit analysis.
if you leave your amp, pre and cd player on all of the time, what is the differntial in cost , i.e., electricity vs turning them on and off as needed.
compare the alleged cost savings in your electric bill with the potential increase in maintaince cost.
i'm not sure how you would estimate the latter. if one could accurately predict the maintainace costs, one could make a rational decision as to whether to leave equipment on all the time.
i think its highly conjectural which of the two approaches is most effective.