This button is for all the window management operations. It is best to use Smalltalk's window management functionality to manage Smalltalk windows. The title bar of a window always belongs to the window manager of the windowing system that you are running. Therefore, the title bars will look different on a Windows machine than on a Sun workstation running X and the twm window manager. Sometimes Smalltalk has it's own ideas about how window management should be done.
P.S. Always explicitly shut down the Smalltalk environment. Some folks like to end their Unix sessions by just logging out. This counts on the window system to kill off all the applications using windows as it itself dies. Sometimes Visualworks doesn't die off after you kill all the windows. In fact if you just close all the Visualworks windows what you have done is deallocated all the objects that these windows represented. Smalltalk, the environment is still running. And now that you have removed all the windows you have no control.... except to kill of the process from the Unix shell. (i.e. this is not a good idea)