Let me just expand on the first two answers (both of the right, of course).
Having the Taskbar show more than the default one line can be a big help,
especially in these days when people are likely to have a lot of software
running at any one time. But as you say, it does take up screen realestate.
So, there is a simple way to have the best of both worlds, here. Simply
right-click on the Taskbar and clikc on Properties, then check the box on the
item that says "Auto-hide the taskbar". When you click the 'Apply' button on
the bottom of the dialog box, you'll see the entire Taskbar disappear. Don't
be worried. Bring your mouse pointer near the bottom of the screen and it
will reappear.
This way, you can set the Taskbar to two or three lines and still have even
more screen room than you started with.