My understanding is that while the person wearing is offered some protection with a mask, greater protection is afforded if an person infected wears a mask, to limit the distance of any exhaled air.
Compared to America where masks were only allowed to be removed between bites of food or sips of drink, in Australia people seemed to be ok with keeping the mask off for the entire meal, or while ‘nursing a drink’. Limiting their effectiveness? This was especially evident in airport lounges and in the airport outliers.
In my experience as early as March there was someone right behind me in the jetway, not socially distancing, who had their mask off while making a phone call.