It means the rocket doesn't have to reserve fuel for a landing burn, and has more leeway in how it positions itself after re-entry, since the helicopter can move at least a bit to intercept. (NB SpaceX Falcon 9 boosters are too large to be snagged in midair by any extant helicopter -- and conversely, RocketLab has already announced that they'll be attempting SpaceX-style propulsive landing for their upcoming, much larger Neutron rocket.)