Comment by selfsimilar

The best training for immune robustness is going outside and get exposure to a wide range of stuff. But for indoor spaces, air quality is going to be dominated by the microbes and viruses of the people in the space itself. For public spaces and shared residential spaces with poor airflow this would be great - grocery stores, nursing homes, etc. For condos, apartments, SFH, etc. it's probably less necessary, but probably wouldn't hurt. Or nice to have when company comes over, or someone in the house is sick and "polluting" the air.