People aren’t moving around the country as much as they used to do. It’s a fact that has occasioned some comment here, as in other places, with most attention dwelling on the connection between geographic and economic mobility. David Beckworth asks a question I haven’t seen anyone else consider: Has declining mobility made the U.S. less of an optimal currency area?

Michigan and Texas have had very different trajectories for their economies. Does it really makes sense for them both to get the same monetary policy?
According to the [theory of the optimal currency area], the answer is yes under certain circumstances. The OCA says it makes sense for regional economies to share a common monetary policy if they (1) share similar business cycles or (2) have in place economic shock absorbers such as fiscal transfers, labor mobility, and flexible prices.

It follows that all else equal, the less mobility between different parts of the country the less it makes sense to have a common currency and monetary policy.