Throwing a weapon from a moving vehicle toward a stationary target can be very effective, if you hit. Every 10mph of speed relative to your target grants a +1 die bonus to the throwing roll.
If you are driving at the time, you must succeed at a Dexterity + Drive roll penalized by -2 to keep control of the vehicle as you throw. The vehicle's handling is not added to this roll. The Stunt Driver merit lets you automatically keep control without a Drive roll at all.