higher RON fuel gives better performance (and mileage too) because it has more ability to be compressed in the cylinder before detonating...
the bottom line is, if you are happy with the per kilometer mileage to fuel price ratio , and it does not hurt your wallet.. there's no harm otherwise in using higher RON number than recomended .. it's bad for engine health to use lower RON, but higher (to a certain level) would not hurt the engine.
oh, so you have a Swift... yes the car runs perfectly fine on regular fuel and does not require high octane; however, if you can afford it.. the engine wouldn't mind it at all : )
btw, what mileage are you getting from it and what is the difference between both mileages ?