Postal Pleasures Presents: St Kilda is an archipelago far off the Northwest of Scotland. These Cinderellas, or labels, as some people call them where produced for collectors and never intended to be used as postage.
Postal Pleasures: Cinderella Stamps – Episode 2 – St Kilda (Scotland)
They were intended to offset the cost of transporting the mail to the mainland postal network and to raise funds for the National Trust for Scotland, so yes, they did serve a purpose!