You could do that, but it will mean that when the tank is full, all of the water will simply go to the waste stream from the RO, with the waste valve still half closed (as it should be when producing pure water). I've no idea if that is bad for the RO or not.
So although the water will stop going into the tank, waste water will continue to be produced.
It is better to have it so that when the tanks full the water into the RO is stopped, so that no more pure or waste is produced.