This one is thanks to the ladies from http://www.wickedgoodtraveltips.com/
As a woman traveling weekly I have to balance safety and convenience. The safety people say “Never leave your key in the folder/envelop with the room number” because if someone finds your packet they know the room number AND have the key.
The convenience part of me says “I can barely remember what city I’m in. How can I remember the room number if I separate them?”
The Wicked Good Travel ladies said to compromise: keep the key in the key jacket, but tear off the number and put that in your wallet so they are separate, but still accessible.