Tags are a strict superset of folder functionality. There's nothing you can do with folders that you can't do with tags. You want nesting? Tags can nest. You want visual clues? Tags can have visual clues. Folders can be and sometimes are implemented as tags.
Well, tags and folders are identical. You can have the same file linked to from multiple folders at once. `ls` will even show you the number of folders the file is part of in the second column.
