Quantity thresholds on products allow you to disable products when they hit a certain quantity.
This is useful when you're integrating with a POS system. Dispense automatically syncs with POS systems every 10 minutes. While this is typically short enough to keep products between Dispense and your POS in sync it's possible that products can oversell because of the lag time between syncing.
Setting a quantity threshold can help alleviate issues with overselling.
To use a quantity threshold on a product go to Menu > Products and click on a particular product.
Click on the Pricing tab and enter a number into the Quantity Threshold field:
You will need to experiment with the right number, but typically a low number like 4 or 5 is sufficient.