Adds a visual indication of what each element is, without needing to write a description for them. If you want to be organized, that is a huge time saver. Every element type in your structure panel on the right side will have a different and easily recognizable Icon. Having a visual indication for the items in your structure panel will help you recognize and spot them faster.
Structure icons is a separate feature and it can be enabled and disabled inside Swiss Knifes Features page under .