A part of the beauty of the Mac OS is that Apple and software developers alike more or less adhere to some basic forms for the creation of icons for items that will be placed in the System Folder. Extensions are created in the form of a puzzle pieces, Control panels have a little slider at the side or bottom, preferences have two radio buttons that indicate that they contain settings. This elegance is part of what places the Mac OS on a level all its own. The third set of icons are those that are manually placed on a document or folder. Custom icons rarely perform any function besides providing something cool to look at or as a visual descriptor of the contents of a certain folder or file.
Icons are just little pictures.
I will occasionally get questions about how the picture that is on a certain icon effects its functionality. Like why do some control panels have the little slider on the bottom and others have it on the side. Or with system extensions, why some are a vertical puzzle pieces and others are horizontal. At the core, all icons are is little pictures. They have no impact on the functioning of the files they represent.