The basic drive of Human Computer Interaction is to provide usable user interfaces. The need for HCI is obvious: if people cannot use the computer system, then it is rendered useless, no matter how "beautiful" the underlying code is.

(To Be Completed, I just happen to be studying HCI right now and saw this pop up on the New Writeups... If anyone is interested, the text is "Human Computer Interaction" by Jenny Preece, ISBN 0-201-62769-8)