The leaf boundary layer
Trapped film
Leaf hairs hold a thin layer of air that is not the same as room air
Used up
That film loses CO2 and gains oxygen and humidity as the leaf works
Stall
Until fresh air replaces it, photosynthesis slows even if the room meter looks fine
Need
Cannabis depends on currents to keep that micro-environment renewed
Movement builds stems
Outdoor model
Wind makes tiny stem breaks that the plant repairs thicker than before
Indoor risk
With no resistance, stems stay weak
Daily flex
If fans are limited, shake stems by hand each day
Pest side benefit
Moving air also makes it harder for insects to settle
Fan placement
Through the canopy
Put fans at or below canopy height so cool air actually crosses the leaves
Reverse overhead
Ceiling fans can run so they pull air up instead of only blasting down
Ventilation
Exhaust to the outside may be enough movement if the room is small
Screen intakes
Filter intake fans so pests do not ride the breeze in
Heat and odor extras
Light heat
Circulation also strips the hot pocket sitting under lamps
Quiet efficient fans
Small inline fans can move a lot of air without a huge power draw
Do not gale
The goal is a steady sway, not shredded leaves