Don't waste space. Waste not, want not. A wasteful walk is an excursion into the realm of destitution.
Be thrifty with your space. A pixel saved is a dollar earned. Thrift, in short-shrift, is a gift!
Every reasonable adult has a toolbox. In this box, you carry an assortment of tools which, given the occasion, are extremely useful. Perhaps you have an adze for squaring up posts, an awl for punching holes, or an axe for chopping down trees. But you don't always square, punch and chop. Even a lumberjack doesn't need quick access to his axe all the time. A lot of the time, carrying around heavy and cumbersome tools is a hinderance. It's nice to have someplace to tuck them away for later use. God bless the toolbox.
On this tack, it's clear that menus which are rarely used on a computer system shouldn't be displayed by default. The Hide Menubar extension for firefox does just this. It enables a smoother browsing experience by enlarging the web page viewing area of the browser, thereby giving users access to more simultaneous information. It's a fantastic product.