Connie Willis, on a convention panel a long time ago, complained about the lack of words for human expression. It's one of the fundamental problems of character-driven writing, how to convey the 75% of information you'd get from a conversation that is not in the words. Imagine just the dialogue of a novel, floating in space, without the grounding of dialogue tags, actions or expressions.
Writers' workshops tend to frown upon repeated use of looks or glances, references to how someone smiled (a sly smile, a ghost of a smile), or "said-isms"--dialog tags that try to convey tone or meaning outside of the words, like "threatened", "cajoled", "whined". Can they be overdone? Sure. But they are also trying to fulfil a needed function. If you watched a play or movie, or simply two friends conversing, you would know all about their history and their attitudes by listening to the tone of voice and observing their body language. The distance between them might speak volumes, more than the words they say.
And the writer must describe all of this, or at least, enough of it that you, the reader, glimpse the subtext, all those nuances that bring the deeper meaning to the words, and bring the characters to life. The moment when someone's eyes meet another's--or dodge the glance--could be devastating.
Some of my favorite moments in films are these little moments that pass between two people, and I often think back on them when I'm trying to capture such moments on paper. The weeping creature-keeper in "Return of the Jedi" transforms Luke's victory into an intimate tragedy. The herald reaching out to the king who is his enemy in "Henry V", even though they never touch, demonstrates the meaning of sympathy and courage. And my favorite scenes in my own words are those where I believe I've expressed something deeper, something that words alone cannot say.
-- Elaine Isaak