It was more than just a special icon for a folder, it had special behaviour too. Without looking it up (in the spirit of the meme), I seem to remember that it would automatically sync the files any time that you insert the floppy disk, kind of like having Dropbox but without the internet. The idea being that you would have files on your computer that you could take with you somewhere else (in your briefcase, on a floppy disk) and all instances of that briefcase would automatically sync the latest updates of the files without you having to manually copy them and work out which was the latest version of a file.