I have to admit that I use CO2 while out riding roads for the simple reason that I can't use a hand pump up to high enough pressure for my road tires (lack of upper body strength). So I have a standign (floor) pump for pressurizing my tires pre-ride, then the CO2 for road emergencies. Although at the end of the day due to funny things with gas, you will need to repump the tire with air (which is mainly nitrogen and oxygen).