What does it actually do? I thought it might be when you have a label as an image, if the image doesn't have a background (transparent background) that that part of the label will be see-through, though I have tested it and it didn't work

Sorry if this is in the wrong area, wasn't sure where to post it as I don't think this is a "Code Problems" or "Developer How-To" related question
It's a developer how-to :P

Either way, it would probably be better if you just experimented. It's very simple, and you should understand it nearly instantly; it makes the background completely transparent, no matter what.