Are you saying the masks are helpful to prevent contraction of the virus, or to stop the spreading of it from those who are contagious, but don't know about it yet?
There is a very succinct explanation by Michael Osterholm [1][2] where he says that the virus is spread both by droplets & aerosols, and that sharing the same air with another person is the primary vector (that isn't intended to sound as alarmist as it probably does).
From what I understand the best prevention is to reduce face-to-face contact with other people where possible, but an N95 mask would definitely help prevent contraction in public spaces.
Of course, these measures seem extreme since ~80% of people will barely notice they are infected / have mild symptoms, but it's all about peak-load reduction.
Wearing a mask to prevent contracting it is like wearing medieval platemail to protect yourself against an M16.
It gives you very limited protection. There's no replacement for just avoiding people, 15 feet away from everyone.
They're mainly good for people who are infected to not transmit pathogens.
When doctors operate on infectious people, they wear hazmat suits. Full face mask, air filter and body condom. You can get a virus through your ears, eyes, mouth, nose, or microabrasions on your skin.
You can wear a mask, but I fear that people will start thinking it's anywhere near full protection. False sense of security is probably not worth even encouraging in a situation this dire.
Masks definitely helpful to stop spreading it from those who are contagious. If they help prevent contracting it depends a lot on how disciplined you are at using them. If fiddling with a mask, you're more likely to contaminate it and yourself.
