Ctrl-Shift-L goes through all enabled layouts. A layout specifies how the "windows" are arranged. Simple splits are available among others. I like the stacked layout: window 1 fills the full height on the left half of the screen, all other windows are stacked on the right half.

There does not seem to be a way to control the borders within the layout with the mouse; e.g. temporarily resize window 1 in the example above to be 80% of the width. That's something I sometimes miss. It's configurable, of course, but not ad hoc.