曼昆哥原话是这么说的：A third policy rule that is often advocated is inflation targeting. Under this
rule, the Fed would announce a target for the inflation rate (usually a low one)
and then adjust the money supply when the actual inflation deviates from the
target. Like nominal GDP targeting, inflation targeting insulates the economy
from changes in the velocity of money. In addition, an inflation target has the political
advantage that it is easy to explain to the public.读过一遍该看明白了吧。联系上下文，这句话应该理解为“设置通胀率的政策使得**不必通过控制货币流通速度的（直接）方式来调控经济”。要么是原书翻译脱节，要么是你理解有偏差。推荐以后直接阅读英文原版。

那么货币流通速度对经济有什么影响呢？