Your mouse will soon rocket you around your desktop.
Nobody likes scrolling.
A conventional GUI presents icons and text in a hierarchical list format. To see a list of the contents in Subfolder A, you must first click on Folder A. Drill down three or four levels, and the initial lists are off the screen. To view Subfolder B, you must close folders and backtrack. With ZUIs, subfolders need not be buried from view. The entire folder structure, in miniature, is on-screen.