As legend has it, later they had a more practical purpose. The non-functioning buttons on the cuff area of a jacket sleeve may have originally been put there to keep the wearer from using the sleeve to wipe his nose.
When I saw a picture of a family of mermaids on Wedgwood buttons from the late 1700's, I knew these were the fastenings a captain from a well-to-do family could locate and have on his seaman's coat, so I imagined them on Captain Forrester's clothing in A Captain and a Rogue.
Because I didn't know how to get replicas to the cover art department, I didn't describe them in the story. Buttons like these would have been very dear in cost, and not easily tossed aside when the clothing wore out.
I once worked in a retail store, and we had a garment, one only, with a very unique and unusual button. The manager brought the jacket to me one day and showed me where the fastening had been removed.Yes, someone stole a single button from a charity resale shop.
Apparently, not only fictional characters and authors like buttons.
The link for the site which shows the mermaid, her husband and three children on a Josiah Wedgwood blue center button is at: