Saving, rather than spending, such windfalls would help to mitigate against potential overheating and allow the build up of buffers which can be used in the event of future downturns. So, just as fiscal buffers can be used to absorb shocks to the economy, the financial system also needs to have such buffers.
It tells people that the Bank will work as hard as it can to get the economy stabilized and back on track, so as to prevent inflation from falling significantly below target for an extended period. It is that anchor and our independence from government that gives our lending programs the power to stabilize things.