You can use mouse clicks on window mode lines to select and manipulate
Some areas of the mode line, such as the buffer name, and major and minor
mode names, have their own special mouse bindings. These areas are
highlighted when you hold the mouse over them, and information about
the special bindings will be displayed (see Tooltips). This
section's commands do not apply in those areas.
Mouse-1 on a mode line selects the window it belongs to. By
dragging Mouse-1 on the mode line, you can move it, thus
changing the height of the windows above and below. Changing heights
with the mouse in this way never deletes windows, it just refuses to
make any window smaller than the minimum height.
Mouse-2 on a mode line expands that window to fill its frame.
Mouse-3 on a mode line deletes the window it belongs to. If the
frame has only one window, it buries the current buffer instead, and
switches to another buffer.
C-Mouse-2 on a mode line splits the window above
horizontally, above the place in the mode line where you click.
Using Mouse-1 on the divider between two side-by-side mode
lines, you can move the vertical boundary left or right. Using
C-Mouse-2 on a scroll bar splits the corresponding window
vertically. See Split Window.