Note: This button will allow you to isolate one object and make all others unelectable until deactivated.
This will help you select one object within a multi-layered composition, without having the frustration of moving objects aside to work with bottom layered ones.
Select the object you want to isolate.
In this image, I'm isolating the image of the watch so I can work with it without having to shuffle my other elements around:
You can find this button in the two highlighted spots in the screenshot below:
Now that it is in isolation, you won't be able to rotate, scale or even move the other elements on the canvas.
To turn this off, simply click the isolate button again.