China is currently amassing large foreign reserves while imposing internally capital controls. Does this make sense? Wouldn't an economy that has the ability to create such surpluses want to participate more fully in world markets? One should not forget that these foreign reserves are accumulated thanks to a positive trade balance and a fixed exchange rate, not thanks to a particularly well functioning capital market in China. In fact, the financial sector in quite under-developed in China, and most households have access to nothing more than simple bank accounts.
Philippe Bacchetta, Kenza Benhima and Yannick Kalantzis build a model where the central bank has access to world market, but domestic households not. This enables the central bank to impose a different interest rate than the world interest rate, but it steady-state it is best to replicate an open economy: accumulate reserves and issue domestic debt at the world interest rate. If the economy grows rapidly, though, you want to have a higher interest rate domestically while imposing capital controls, that is, one needs to prevent arbitrage. But then, intertemporal substitution needs to happen through international reserves, as households cannot do it.
What is intriguing here is that we have a situation where open markets are welfare inferior to restricted ones with a reserve accumulation policy. Usually, we think that free markets would work best, especially as here there is no moral hazard, systemic risk, or other distortion. The reason is that borrowing constraints are binding as the economy converges towards steady state, and it cannot provide adequate intertemporal allocation in open markets. The central bank needs to help, and needs to differentiate interest rates to do so. That can only happen with capital controls.