Been wondering this myself. In my mostly uneducated mind, something to remember is that if you "print" money and give it to people, there's no way to really get it back (that is, control the money supply in both directions). Sure you could just increase taxes but taxes can't even cover the budget, let alone decrease the money supply.
If the Fed instead purchases assets such as MBS, corporate bonds and especially Treasury bonds (yes, the biggest owner of US government debt is actually the US government), those assets can later be sold. The Fed can then pull the money back out of the supply for future use. Assuming of course that high risk MBS and junk corporate bonds don't expire worthless.
If the Fed instead purchases assets such as MBS, corporate bonds and especially Treasury bonds (yes, the biggest owner of US government debt is actually the US government), those assets can later be sold. The Fed can then pull the money back out of the supply for future use. Assuming of course that high risk MBS and junk corporate bonds don't expire worthless.