Competition is the idea; so just as, good turf crowds out weeds, this system supposedly gives grass the edge.
But yes, this is a call to experiment. I do have a patch of grass with weeds, because I never spray my own lawn.
However most of the weeds that survive in established turf are of the basal meristem variety and I don't see stopping them if they have enough root to survive. Then again - I have been surprised before.