That's essentially what zoning is, most commonly used to heat/cool different floors of a house separately without having to have multiple furnaces and AC units.

That's essentially what zoning is, most commonly used to heat/cool different floors of a house separately without having to have multiple furnaces and AC units. If I understand correctly, you want the shut-off flaps or gates as close to the blower as possible for maximum efficiency—just shutting off the vents at the ends of the lines would mess with pressure and airflow in the rest of the system in undesirable ways.