can any1 tell me what does this switch (i read the help file, don't understand..)
Not sure I understand the meaning of the help file too... :\
In a nutshell it will associate itself with the active connection if your using mirc with more than one server. Try opening one /window -i @window and connect to a couple servers and change your point of view from one server to the other and see how the window moves to the active connection.