"Some people with swine flu travelled on a plane from New York to China, and many fellow passengers got infected. Some researchers looked at whether passengers who wore masks throughout the flight stayed healthier. The answer was very much yes. They were able to track down 9 people who got sick on the flight and 32 who didn’t. 0% of the sick passengers wore masks, compared to 47% of the healthy passengers. Another way to look at that is that 0% of mask-wearers got sick, but 35% of non-wearers did."
https://slatestarcodex.com/2020/03/23/face-masks-much-more-t...
At the beginning of the pandemic I was skeptical about the effectiveness of masks and this article is what convinced me that there is some benefit.