The upcoming LEGEND-1000 and DarkSide-20k experiments are examples of neutrinoless double decay and direct dark matter searches that will reach unprecedented exposures of 10 and multi-hundred ton-years, respectively. With this comes unprecedented radioactive background rates, which must be suppressed. Argon sourced from underground CO2 wells (UAr) has been shielded from cosmogenic activation, and provides a powerful medium in which large, rare-event searches can be effectively performed. The crucial role UAr plays in the LEGEND-1000 and DarkSide-20k experiments will be emphasized. DarkSide-20k cryogenic experience, proper handling techniques, strategies undertaken to maximize light yield, and other applications in the search for rare events will be discussed.