There are really two things that this makes possible and easier:
1) Share an internet connection with multiple devices.
2) Network multiple computers/devices wirelessly and be able to share files, media and/or printers between devices.
Yes if you have wifi at home, then you don't really need this. However, you must admit this is a neat feature to have, and can come in handy when needed, where previous versions of Windows gave no option of doing this.