Communication about the intentional horizon of net asset purchases and expected future path of the policy rates is a key component of the policy strategy that started in 2014. The reason is simple and, once more, has to do with instrument complementarity.
Above and beyond any signalling content they may have on the intention of the central bank to provide accommodation, asset purchases add stimulus principally by squeezing the term premia priced into longer-dated securities. However, absent reassurance that policy rates will remain anchored around their lower bound for the entire life of the net purchases, the impact of asset purchases may be partly neutralised.