When you're viewing a document in Word, Excel, or PowerPoint, a flick of the mouse wheel scrolls your document up or down, just like in a Web page.
Move your cursor up to the Ribbon, however, and the mouse wheel takes on a different function: It scrolls through the tabs.
I'm not saying this is any faster or easier than just clicking the tab you want to view, but it does give you an alternative.
What's more, it helps cut down on "click accidents," like when you aim for a tab but actually click a tool icon (with disruptive results). Surely I'm not the only one who does this? (Please say I'm not.)
Anyway, give it a try. Firefox users can do likewise: When you've got more browser tabs than will fit on the screen, just mouse over the tabs and spin the scroll wheel to cycle through them.