Do not leave it in "ON" mode. That will drain the battery very quickly regardless of what items are turned off.
I've noticed that the moon roof can only operate when the ignition is ON. It's handy to still be able to roll-up the windows after turning off the engine. It's quite annoying in other vehicles to have to turn the car back on to get the windows to roll-up. However, I still have to do that with regard to the moon roof... and from Spring to Fall, I use that as much as I do the windows. (personally not a fan of air-conditioning and never use it)
Restating other comments: "ACC"essory mode remains in full effect for a period after the engine is shutoff. The radio can be run whenever the key is inside the vehicle. The radio always runs on a power-off timer whenever the ignition is off.
You may be able to manually reset the timer at your convenience (like during a commercial or break in programming) by turning it off and back on.