The C172 POH checklists say to set the fuel selector to "right" or "left" when securing the plane but "both" while operating the plane.
What is the point of changing the fuel selector when the engine isn't running? IOW, what practical (not legal) problems could it cause to leave it on "both" while secured?
[Edited to remove incorrect understanding of the vent connection between tanks, which is cleverly designed to not cross-feed fuel.]