Your canvas can become quite cluttered if you have lots of patterns and geometry. This tool allows you to show and hide layers. Hidden layers are not deleted and can be easily shown again.
It is still possible to add items to layers that are hidden. You may think a tool is not working properly, if you do this. Always pay attention to the layer you are working on.
Select any layer in the tree. If it is hidden, it will show. If it is visible, it will be hidden.