"If you are healthy, you only need to wear a mask if you are taking care of a person with suspected 2019-nCoV infection."
I think that's more a difference between western and east(asian) conceptions and usage of the mask. But I did want to bring it up earlier. In most East Asian countries/China you have people wearing masks, and in these same countries, people were very commonly wearing masks daily anyway, even before the virus. In fact, if you don't wear a mask (especially now) in East Asian countries, while the opposite is true in many Western countries (at least until quite recently, if you were wearing a mask you'd get dirty looks or worse).
As mentioned very early in this thread, aside from the highest end masks, most will not protect you from aerosolised droplets with the virus. When I ask people I know from some East Asian countries (admittedly not medical professionals), the response was very often "What if someone sneezes on your face?!"
I've got to say, in my entire (reasonably long) life, I've never had anyone sneeze on my face, but if they did, yes, I suppose masks would help prevent me from catching infection from them (probably wouldn't be covid19, because that virus doesn't cause sneezing).
These masks definitely prevent you from spreading the diseases to others, so in that regard, they absolutely help, especially in the early stages of your infection, when you don't know you're infected. Aside from that, I feel the benefits of the mask are definitely there, but mostly incidental. Having a mask makes you less likely to touch your face, or have droplets reach your face, in which case, even if you had a scarf or a cloth mask, or even if you were wearing your mask wrong (which the vast, vast majority of laypeople who wear a mask do), it would be just as effective as an N95 (or higher) for day-to-day use.