Here is a link to a study by the University of Maine's Engineering department:
And a ton of other examples. When ever you are stopping the oil ingestion, the engine does not experience the detonation caused by it, and the ECU/PCM will keep the timing advance at optimum running more efficiently. It is impossible if driven the same not to.
Just ask anyone with a SS that has run 87 octaine in it and the detonation has caused the PCM to default to the low octaine tables. app 4-5% less power and fuel economy.