tape in deck when off????

Take the tape out. Leaving it in the deck is bad for both the tape and the deck. Some of the issues are mentioned above. Your tapes will remain problem-free much longer if they are rewound to the end and kept in their cases when not in use. I also would recommend to take the tape out “before” powering down the deck.

Best regards,

You actually use cassettes still?....just kidding

Depends on the deck. Better decks disengage the pinch rollers when powered down. I can't see much harm in leaving the tape in for such a deck. Leaving the tape in a deck that doesn't disenage the pinch roller can cause the roller to deform from the constant pressure over time - not a good thing.

Although the head typically lifts away from the tape in the off position, the other parts (capstans and guides) do not. If they've not been demagged recently, they could do damage.

I believe that you can leave oxide deposits on your tape passage components (pinch rollers, capstan, and, if engaged, the tape heads as well); also, if there is tension on the tape segment, some stretching of this segment of tape may occur, especially if the tape was shut off while engaged in the play or record modes. I'm not entirely sure, but if the tape is stopped (using the stop button) no harm will come except some minor deposits on contacted areas, which can be easily cleaned during the periodic routine maintainance, so, I guess it all depends on just how the tape was left in the deck, and just how the deck was turned off. Anybody else with some thoughts on this?