There are several applications which I use zoomed so I can have the maximum available space to work. Sometimes I even hide the toolbar, but this causes the window to resize too, reducing its size. But if you zoom the window again, the toolbar now can be shown and hidden without changing the size of the window.
BTW, although I guess this is common for previous versions, I'm working on 10.5.6.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090103081416586