Which one is a unique feature of mutual funds or ETFs?

The question describes a feature of asset allocation funds, which exist as both mutual funds and ETFs. A key, unique benefit of these products is their automatic rebalancing. The fund manager periodically buys and sells the underlying assets within the fund to maintain its target asset allocation (e.g., 60% stocks, 40% bonds). For the investor, this rebalancing is automatic and does not trigger personal trading costs or immediate capital gains tax events, which would occur if they were to rebalance a portfolio of individual securities or ETFs themselves. This convenience and cost-efficiency is a primary selling feature.

A. While holding a consistent asset mix is the goal, the automatic rebalancing is the unique feature or mechanism that achieves this for the investor without their intervention.
B. Asset allocation ETFs generally have much lower Management Expense Ratios (MERs) than traditional, actively managed mutual funds.
D. Both mutual funds and ETFs (held at a brokerage) are fully compatible with pre-authorized contribution (PAC) and systematic withdrawal plans (SWP).

1. TMX Group. (n.d.). Understanding Asset Allocation ETFs. TMX.com. (Highlights automatic rebalancing as a key feature: "Asset allocation ETFs... offer a simplified way to build a diversified portfolio that is automatically rebalanced").

2. Ben-David, I., Franzoni, F., & Moussawi, R. (2017). ETF Arbitrage, Non-Fundamental Demand, and Return Predictability. Fisher College of Business Working Paper No. 2017-03-02. (While technical, this paper discusses the internal mechanics of ETFs, which includes the portfolio management and rebalancing done by the manager).

3. McGill University. (n.d.). Personal Finance Essentials Course: Module 5 - Investing. (Courseware often explains that a key benefit of balanced funds and asset allocation ETFs is the professional management that includes automatic rebalancing).