Circulating air brings several benefits to your plants. The most noticeable is that the air beneath grow lights begins to heat up, raising the temperature around your plants above the 72°F that is at the top of the ideal range for their health.
Moving out the stale hot air and bringing in fresh air with a fan keeps your plants cool. It also delivers a steady supply of carbon dioxide, which plants breathe in through their leaves.
A gentle but constant breeze also encourages your plants to grow strong, sturdy stems, the foundation for a hefty harvest of flowers or fruit.