I strive mightily to keep the bike light against my sweetie's tendency to put more and more small things into the bags. A 19mm is pretty heavy. Plus I'd need a 10mm, preferably a socket and ratchet, to unhook the drum cable, and a 9mm (or is it 8?) to free the anti-rotation arm. Yeah, we could carry that stuff, already do carry a spoke wrench, a small adjustable, and a small screwdriver. But this is a fairly civilized part of the world. Fools like myself sometimes rely on the kindness of strangers, or at least the kindness of a cell phone call. Failing that I rely on the fact that almost all flats can be patched without needing a completely new tube.