Recall that the purpose of money printing is to encourage or discourage spending. When the central bank wants to encourage spending, they print money leading to inflation. Inflation encourages people to turn cash into goods and physical assets. This increases spending in the short-run and stimulates the economy.

The blockchain makes it possible to execute more powerful monetary policy. Money printing is coarse because price increases occur with a time delay. The blockchain is precise and effective inflation can be achieved instantaneously.

Suppose the central bank controls 51% of hashing power and wants to achieve a stimulus equivalent to a 3% increase in inflation.

Simply demand a txn fee equal to 3% of coin-age (with age measured in years). This is just like instantaneously increasing the inflation rate by 3%. Take the fee proceeds and hand them out to banks. Voila. You have stimulated spending. Once the economy recovers, the txn fee can be lowered again. The inflation rate of every single block is completely at the bank's discretion. This is 100% impossible with the tools available today.

Now people might try and horde (the bank can't steal my coins... I'll just wait till they lower the fee and spend then). Ha, this would not work at all.
The bank has a historical record of its inflation policy and would bill these guys. The fact that you haven't paid yet won't help them. The seignorage will be deducted from their account whenever they finally decide to spend. [Could go through more details on calculating seignorage fee, but I think that is enough for now.]

It is pretty clear that the blockchain gives central banks unprecedented control over monetary policy. All they have to do is command 51% of hashing power. An absolutely negligible investment for such a well-capitalized institution.

I am kind of confused why we still operate with dollars. Central bankers should start issuing dollars and euros this way. Or they could just adopt bitcoin. It would make their lives so much simpler.