From what I know about Covid-19, it is spread through water droplets in the air we exhale. If that’s the case, if we can limit how far the air we breath reaches than that should limit the radius of infectivity. I’ve seen videos showing sneezes and the aerodynamics of our regular breathing without any mouth or nose covering. The distance things can travel without a barrier is pretty far. I believe a simple barrier, like a mask, can block the trajectory and significantly limit the distance these particles can travel.
There are 3 means of slowing down the spread of the virus:
1. Social distancing
2. Washing hands with every contact and every hour irrespective of contact.
3. Masks. There are 2 types of droplets. Big ones that are gravity-driven to surfaces where they die in minutes (outside sunlight) or days (smooth metal surfaces). Small droplets that aerosolize as fomites and get transmitted from person to to person. All masks work on the big droplets. The quality of the mask matters for the fomites.
It is not a straight forward discussion. Remember that this is a very contagious virus (not measles contagious but still up there). This means that most of us will eventually get infected. All we are trying to do is slow the rate of infection enough that we do not exceed hospital capacity and to protect those with a serious risk of death (over age 75 with a comorbid condition).