I'm not sure what effect that would have on fuel consumption but I do know that it has a huge effect on performance.
What some people believe is that because they don't "hear" or "feel" any pinging there isn't any. That's far from the truth. Sometimes you won't hear any knock/ping but the knock sensor will pick it up. You will be smiling and pushing the car while the ecu will be fighting hard to prevent further knock.
This behaviour can easily be seen by plugging in any device to the OBDII port that displays live data.
It will show knock counts/timing retard/high knock control even though you may not notice it at all.
Honda knock control is designed to cope with different quality fuel in a stock engine. The ECU has the ability to retard the ignition further if it determines that knock is occurring. From the amount of knock sensor noise, and knock sensitivity, the ECU adjusts a 'knock control' ( or 'K.Control') variable. Nominally the 'knock control' contains the estimated fuel octane, as a percentage of the difference between 100 and 90 octane. eg a value of 0% means the ECU considers the fuel 100 octane or above, a value of 25% means the ECU considers the fuel to be 97.5 octane. The K.Control is dynamically adjusted while you drive.
Sometimes your knock control value will be really good and the moment you fill super or hobc from a shady pump the value shoots up. If you have a device capable of showing you live data, you will never go near super.