Viewing
Option + clicking the eye icon of a layer is a commonly known way to hide
or show all other layers. There is also a way to expand and collapse layer
groups: by Command + clicking the arrow next to the layer group, you can
close or expand all other layer groups; this does not work on nested layer
groups. Alternatively, right-clicking the arrow gives you a menu to perform
the same actions; but this will only work on nested layer groups.