In which should I let my gears when not biking? I heard from a friend I shouldn't let my bike "resting" with the combination biggest front ring and the smallest back ring because in his words "it keeps the system under tension". 

Does it make sense?
How should I let the gears?
Don't worry about it, it really doesn't matter what gear you leave it in.

Can't comment so, this is a duplicate of this.