Unless a person is exceptionally skilled at being artful, their facial expression will reveal a lot about how they feel and what they think. It depends on context, but it is important to maintain eye contact with a person during communication.

A person's face can reveal when they don't agree with you, when they don't like you or when they are lying, for example, during communication. I personally make it a point to monitor someone's face whenever I communicate.

It makes communication so much more effective and predictable. Of course, you can't really rely on it for everything, but it helps out still. It is worth the effort.