We all wear uniforms most of the time, willingly or not. I suppose you might say my usually casual dress is my uniform. A suit and particularly a tie are the uniform of the conformist. Costumes are often uniforms of pseudo-non-conformists. By definition, true non-conformity is only a rare, momentary impulse. (Conformist, pseudo-non- and sometimes non-, exist in each of us and come out at different times.) Sometimes costumes can be a way to get into different states of consciousness. But there are easier and cheaper ways to do this.
Masks (broadly defined) represent our "need" for privacy and secrecy, ways to hide our real selves. Intimacy and privacy seem to be at opposite ends of a spectrum.
But why should we need to hide ourselves? Because we've been raised in a culture that hides. We haven't had much chance to observe others in certain circumstances, and therefore to develop standards of what's proper. So we are afraid that we are different, and that others won't approve.
Status symbols are a way of flaunting how much we can afford to waste, and therefore how much we claim to have in reserve.
I've heard that small talk is an excuse to be in each other's presence for a little while so that we can read each other's body language. But then there are lots of books and classes on body language, apparently so that we can learn to lie to each other in this mode of communication while exchanging inanities verbally. I've never trusted body language much.
Rituals are part of our tribal orientation, a way proving that we are really one of the group (closely related to uniforms).
When we concentrate on these modes of socializing, we make true intimacy very complicated.