interior finish

Back in my days as a classical guitar player, some instruments had a wash coat of finish on the interior of the body. My guess is that it was purely cosmetic. It did make the interior very clean looking. Any comments?

There was a recent related thread here on interior finish.
http://www.ukuleleunderground.com/forum/showthread.php?58300-a-couple-questions-of-wood-and-humidity&highlight=finish+inside