I have worked on the U.S. policy response to every major financial crisis over three decades. I served at the Department of the Treasury as part of the team responsible for supporting America’s recovery from the Global Financial Crisis and responding to the euro-area financial crisis.
For example: letting the expectations component of longer-term yields float upwards while, at the same time, engaging in asset purchases would be an inefficient conduct of policy. The compression of yields through the asset purchases would be directly countered by an upward drift in the expectations component.