Apart from SEO usage, it is the label that appears at the top title bar. In latest browsers we see it in the tab, which is not much useful as a lot of it is not visible due to small width of a single tab and we have multiple tabs at any given time. But in old days the title of the window used to take the whole width, and show a brief description of what the page contains. It has kind of lost its charm and is only left for SEO. We used to feel happy by using some javascript to put some effect in the title e.g. scrolling, blinking etc.