No, it helps both ways. Someone's spittle from talking/yelling doesn't so easily land on those around them, if they are wearing the mask, and it wouldn't easily land in the mouth/nose area of those close by, who were also wearing a mask, regardless if the one doing the expelling was wearing one or not.
But obviously the more that wear them, the less body fluids are ejected onto people and objects nearby, reducing the chance of spreading the contaminated fluids, with the added benefit of subsequent face touching having an extra barrier.