Thanks a lot for help! I was afraid that nobody would ever spend some minute to read and answer my post :-)
Ok thank you for clarifing that no other rewards for staking Leo.
So Hive Backed Dollars (HBD) can be used for some kind of market of NFTs and other stuff or can be "redeemed" for Hive simply sending to a "fake" user 
That's really good infos. But still the point:
why staking HBD then?
Sorry maybe I missed something
RE: Am I stupid, or what? Can't fully understand LeoFinance mechanisms