A: The Adjustable Flow Restrictor is typically used for hobbyists with booster pumps or higher municipal water pressure. It allows them to dial in a more efficient waste-to-water ratio. If the TDS of the source water is high, a higher waste-to-water ratio is better to help the RO membrane last longer. If the TDS of the source water is lower, you can adjust the system for a lower waste-to-product water ratio to save water.
Please do note that this will not resolve issues caused by low water pressure. If your water pressure is 60PSI or lower and you would like to have more product water (or have less waste water), the solution is to add a booster pump.