The problem is that when unpowered the input circuits of the deck can load down line level signal in the preamp, often resulting in a loss of highs. Whether or not this is an issue depends on the architecture of the preamp.
If the preamp has buffered recording outputs then the deck is isolated from the rest of the preamp circuits and you don't need to power it up unless you're using it. Otherwise it's best to power the deck up or disconnect it during listening sessions.
This is only an issue for devices connected to the preamp recording outputs, and doesn't apply to input devices such as Cd players, tuners, turntables, etc.
If the preamp has buffered recording outputs then the deck is isolated from the rest of the preamp circuits and you don't need to power it up unless you're using it. Otherwise it's best to power the deck up or disconnect it during listening sessions.
This is only an issue for devices connected to the preamp recording outputs, and doesn't apply to input devices such as Cd players, tuners, turntables, etc.