On the iStills 500, 1000, 2000, and 5000, the pre-cooler now comes as standard equipment. On the Potstills, Plates Stills, and Hybrid iStills of those sizes.
The pre-cooler takes the load of the main cooler and improves overall cooling efficiency. The same amount of coolant leads to better cooling. Ideal in warmer climates. Or, by running the pre-cooler and the column cooler from different water lines, one can increase the total amount of coolant used, making cooling more effective.
Nota bene! Distilling is about heating up liquids to the point where they boil and create gasses. And distilling is just as much about cooling those gasses down to liquid phase again. In other words, given the iStill's efficiency, power in basically equals cooling in.
The pre-cooler is no excuse not to invest in a professional sized chiller that provides the same amount of cooling in kWh as the maximum power of your iStill. Without sufficient flow and cold enough coolant (< 8 degrees Celsius), the performance of your still will be affected negatively.