Windows can be grouped in order to :
Use a linked cursor specific for the group ( don't forget to enable Settings => Preferences => Linked cursor => Display linked cursor option).
Handle the same object in all windows of the group : click on View / select objects contextual menu in a window of the group, a browser appears. Select the object in the browser. Note : by default all windows are considered to be in the same group and objects can be selected in all windows via any browser window.
To create a windows group :
Select the windows to link in the windows panel (on the right). For multiple selection, press Ctrl key and click.
Then create the group with Windows => Link windows menu.
To undo a windows group :
Select the group on right panel.
Undo the group with Windows => Unlink windows