I'd leave it on unless there was a danger of electrical storms, in which case I'd switch it off and unplug it. Otherwise I see only benefits in leaving it on ... longevity, sound (maybe), and no downsides (unless it's got a huge power consumption, which is very unlikely).
I leave my integrated amp on all the time, but I turn the volume to minimum and select an unused input when it is not in use.
I leave my integrated amp on all the time, but I turn the volume to minimum and select an unused input when it is not in use.