There are actually several suggestions, which were repeatedly discussed a decade ago in multiple SARS studies (see my post below).

First is prophylaxis for front line health care workers, who are suffering grave infections likely exacerbated by long hours and low morale. Long term use of chloroquine or alternatives is a concern for this audience. There were fatalities last time, just like this time.

The second is for the patients themselves, who will otherwise endure uncontrolled viral replication for up to two weeks until the adaptive immune response recognizes the pathogen. Reducing transmission requires an earlier end to this stage.

Is the data from the previous studies worthless for these goals?