It has been shown that many patients with Coronavirus cannot tell when their oxygen levels are dropping until it is too late. A pulse oximeter is the only accurate way to diagnose oxygen levels at home. Accurate information can allow for early intervention to avoid more drastic treatments such as ventilators.
According to the NY Times "All persons with cough, fatigue and fevers should have pulse oximeter monitoring even if they have not had virus testing, or even if their swab test was negative. A vast majority of Americans who have been exposed to the virus don’t know it."