Carbon can build up through normal driving and cause idle quality problems as well as hesitation on accel, and in some cases cost gas mileage (although minimal). Cleaning injectors on a regular basis is jsut good PM, the factory maintenance guide willnot show it, but many don't show a trans service either and most don't agree with that. In tank cleaners will work over time, some gasoline will build less carbon than other, but it is a by-product of the gasoline engine. Even though its seemingly running fine, doesn't mean you don't need it or it wont help, you change the oil even through it was running fine, same thought. If you would like visual proof remove your air cleaner and look down the TB with the butterfly open, you will see carbon on the walls of the throat.
we tested it in a Hayabusa with lots of carbin on the valves and in 3 tanks 15 gallons the valves were clean! 
