Yeah, I know it will hold air until I get home. That's not really my worry.

My normal method of dealing with flats is that when i flat out on a ride I just swap tubes. Then when I get home I patch the punctured tube and put it back in my pack as the spare and leave the replacement tube in the tire.

My question isn't so much whether a too small tube will work in a pinch, but whether there are any reasons why I wouldn't want to just leave it on the bike permanently if/when I swap out tubes. Am I asking for trouble in any way?