They're using the blockchain to essentially track the authenticity and proper ownership of your "burger points." I'm with other comments that it's complete over

They're using the blockchain to essentially track the authenticity and proper ownership of your "burger points." I'm with other comments that it's complete overkill but your post misunderstands both blockchain and BK's implementation. To start with, there's no mining involved since it's proof of stake. There's so many other identity/trust/authorization opportunities for blockchain so I could see this being a low-risk test case for something more significant one of BK's partners has in mind.