For the average non-healthcare person, a mask of any kind provides a physical barrier from droplets breathed or coughed or sneezed out by another human. Not meant to sterilize the air you suck in. Back in the day at work every clinical person had to be measured for an N95 mask due to the slim possibililty of interacting with a TB patient or a suspected TB (very very few ruled in for TB. If the N95 didn't pass the saccarine test (meaning we could taste the saccarine squirted into an airtight bag put over our head while wearing the N95), we were required to use the respirator with the exhaust motor worn around our waste. However, most garden variety masks such as those shown are useful to remind yourself not to touch your face, especially any area of your face not covered by the mask. And to wash and dry that mask for the next wearing. I forget the size of molecule/particle the N95 will filter. Hardly ever saw anyone wearing one. Mine stayed in my desk drawer.
The surgical mask worn in the OR lasts about 45 minutes as far as keeping the doctor's spit out of the surgical wound. Because our breath is moist, and moisture reduces the barrier though still there is some protection. Same for masks made of cloth...better than nothing in some situations. But we aren't wearing them to protect the other guy, in most cases. Masks make us feel better, like we are actually protecting ourselves. And other people either feel thankful that you are wearing one, or assume you have an illness. Just know it isn't total protection unless you are wearing the full body space suit, face/eye mask (like goggles) in tandem.
If I'm doing direct patient care I want as much protection as I can get. Otherwise, hand sanitizing really often, not touching your face (hard to do) and keeping a distance from others are the best things to protect you. JMHO.
**Edited to say if it is reassuring to wear a non-medical mask for your own protection anywhere you go, wear it. But wash it in hot water (or boil or steam it) after each wearing.
Much discussion going--to wear or not to wear. Nobody can say for sure because it depends on a person's compliance with distancing, hand washing (or foaming), touching surfaces then touching the face.
I saw one person wearing a mask over her mouth but below her nose. Useless.