Yes discs can be left on while its off.
No it wont damage them
As a new Wii owner, I'm wondering if it is ok to leave the game play disc in the console? We only have the one that came with the Wii right now.
yep i leave mine in all the time and had no probs yet
I see no problems with it, although as a precaution..take it out. Or you would rather learn the hard way? When leaving it in while the Wii console is operational, when knocked over it could scratch up the disc rendering it unreadable