Originally Posted by
ThermionicScott
Leaving it on is a convenient way to make sure it's always around. Just don't forget to take it off and tighten the Presta locknut again after filling. Loose Presta locknuts can allow the valve to jostle open momentarily and lose air.
Yes, leaving the converter on is no big deal (unless you're a weight weenie worried about the rotating gram that unbalances your wheel), but after inflating I would take it off, close the Presta valve, and put the converter back on, otherwise the valve could be very leaky