The SBD(Steem Dollar) serves a few purposes.
- First and most importantly, this SBD is the currency that Steemit creates and issues. Steem is created via "traditional mining", not the way steemit creates and rewards SDB and SP. Buying or mining massive stockpiles of Steem and distributing it would be costly.
- SBD is pegged to the USD so that people can simply understand the approximate value of their post.
- Allows you to liquidate SBD immediately via trade or market.
- Stability.
- Diversity.