Class A is treated as Tube's, never leave it on, it will not only suck down the juice, but will create a lot of heat, and in this case will definatley from the heat standpoint create faster wear of some parts... However this could be the opposite for some A/B designs which pull next to nothing at idle and simply run basically in standby with no heat, not all but some are this good and efficient, in turn you could leave on Solid state CD players, Preamps for extended periods of time and possibly get a little better sound reproduction from 8-12 hour warm up periods and will not wear them down much, it is possible not absolute so lets keep the Flames off on this topic.