Pro: Leaving any component on all the time tends to keep everything thermally stable and avoid thermal shock: light bulbs fail most of the time when they are first turned on.
Con: Some amplifiers (e.g. Krell class A rather than class AB push pull) run so hot in idle that turning the amp off while idling is recommended by the manufacturer.
Con: Some amplifiers (e.g. Krell class A rather than class AB push pull) run so hot in idle that turning the amp off while idling is recommended by the manufacturer.