Rolling up hides the contents of a window while leaving its title bar visible. You can thus readily see that the window is still present on the desktop while reducing its "footprint" to a much smaller size on your screen. In addition, windows so represented by only their title bars remain fully active: i.e., you can move them, minimize them, call up their system menus, or simply close them.
Hint The Roll Up action is ideal for situations when you work with several opened windows simultaneously and need to quickly review the contents of an inactive window presently underlying the active one. Simply roll up the obstructing active window, review the information uncovered in the previously obscured window and then unroll the active window back down again.