This reformulated guidance succeeded in anchoring expectations about future short-term rates despite the end of net purchases and, therefore, contributed to keeping longer-term interest rates low. More generally, by using rate forward guidance, central banks can do what they also do when employing asset purchases, namely to influence long-term rates and stimulate the economy when conventional policy is constrained.
Besides shaping expectations, asset purchases can work through other channels, such as portfolio rebalancing, as well. But they also entail different risks and possible side effects, all the more so in a monetary union with fiscally autonomous member states.