George Pennacchi discusses narrow banking in an article in the Annual Review of Financial Economics. He concludes as follows:
During the nineteenth century, US banks were more narrow than they are today, and the narrowest (e.g., those under the Louisiana Banking Act of 1842) appeared resistant to panics. Common modern-banking practices, such as maturity transformation and explicit loan commitments, arose only after the creation of the Federal Reserve and the FDIC.
… There appears to be little or no benefits available from traditional banks that could not be obtained in a carefully designed narrow bank financial system. Most importantly, a narrow-banking system could have huge advantages in containing moral hazard and reducing the overall risk and required regulation of the financial system.
In contrast, the reaction by US regulators to the recent financial crisis was to expand the government’s safety net by raising deposit insurance limits and by giving more financial firms access to insured deposits. Expanding, rather than narrowing, the activities that are funded with insured deposits is justified if one believes that regulation can contain moral hazard when firms have many, complex risk-taking opportunities. Unfortunately, this belief appears dubious if one recognizes that regulators face political and information constraints.
In my view, there is a need for research that considers the optimal design of a financial system when a government regulator is limited in its ability to assess risk. … Research needs to better identify those financial services where government support would produce a net social benefit. Services such as maturity transformation and liquidity insurance may not deserve costly government guarantees. Finally, should further research support the general concept of narrow banking, there are still open questions regarding the specific features of these banks. In particular, how narrow should be these banks’ assets and should their liabilities should be deposits or equity shares (at fixed or floating NAVs) are questions that need better answers.