A tool for developers to see the different depth of elements and its position in the DOM.
The problem is that unless the element on the page has a solid background or it is a picture, you do not see how does it fit into the layout, e.g. most of the text nodes, pictures with transparency, etc.
With the above extension you will see the different depth of nodes, it will use different color allowing you to see the size of each element on the page, their margin and their padding. Now you can easily identify inconsistencies.