Any idea what the purpose of the "promo code" is in the game's option menu? (Where you adjust the volume and quit the game)

I am Bread!
A physics based game where you're a slice of bread that has to get to the toaster and toast itself without touching the floor because yuk!
http://store.steampowered.com/app/327890/
Just entered early access and people seem to actually like it!
Seems like an interesting Octodad / QWOP type thingy