Specifying "&global_" in window name

Some time ago - sorry my memory has failed me - I had a display problem in a CHM - I think - that was solved by adding by adding $global_ to the start of my display window (e.g. $global_window1). As such I have religiously added this to all my windows on new projects ever since. I'm now wondering if this is necessary. I've tried searching on the forums and elsewhere but can't find any mention of what $global_ does or whether it is indeed necessary. Can anyone shed any light?