Converse with fellow players
By default Circle is set to Access/Cancel:
Just like on Keyboard, Access lets you interact with objects/terminals/etc. (And pick up items.) This is why it has no function.
@coldreactive When Not Accessing Anything I.e On The Field
Not possible, since you have to be able to pick up items. One of the biggest strategies in this game is to use a --mate item as a Health pickup, rather than stock them.