COVID-19...see the attached link. Also, while no mask is 100% effective, good masks (e.g. KN95/N95) definitely reduce the "Viral Load" someone might get, which means the severity of any transmitted disease will be less and help keep the individual out of the ICU and Morgue.
You've seen yourself how Baron twice screwed up over Masking...a) on the MIT Report he failed to read their conclusions that Masking was Highly Valuable, and b) in the NEJM Report, he couldn't even comprehend that it was a full blown study with tons of data backing up their conclusion that Masking was very effective in Boston schools. BVZ demonstrates a considerable degree of laziness in his posts, and therefore erroneous conclusions/opinions...but it's your choice when decision time comes.
Link: https://egc.yale.edu/research/largest-study-masks-and-covid-19-demonstrates-their-effectiveness-real-world