The most obvious advantage of index funds is that they have consistently beaten other types of funds in terms of total return. One major reason is that they generally have much lower management fees than other funds because they are passively managed. Instead of having a manager actively trading, and a research team analyzing securities and making recommendations, the index fund’s portfolio just duplicates that of its designated index.

Index funds hold investments until the index itself changes (which doesn’t happen very often), so they also have lower transaction costs. Those lower costs can make a big difference in your returns, especially over the long haul. “Huge institutional investors, viewed as a group, have long underperformed the unsophisticated index-fund investor who simply sits tight for decades,” wrote Buffett in his 2014 shareholder letter. “A major reason has been fees: Many institutions pay substantial sums to consultants who, in turn, recommend high-fee managers. And that is a fool’s game.”

What’s more, by trading in and out of securities less frequently than actively managed fund do, index funds generate less taxable income that must be passed along to their shareholders. Index funds have still another tax advantage. Because they buy new lots of securities in the index whenever investors put money into the fund, they may have hundreds or thousands of lots to choose from when selling a particular security. That means they can sell the lots with the lowest capital gains and, therefore, the lowest tax bite.

The Drawbacks of Index Funds

No investment is ideal, and that includes index funds. One drawback lies in their very nature: A portfolio that rises with its index falls with its index. If you have a fund that tracks the S&P 500, for example, you’ll enjoy the heights when the market is doing well, but you’ll be completely vulnerable when the market drops. In contrast, with an actively managed fund, the fund manager might sense a market correction coming and adjust or even liquidate the portfolio’s positions to buffer it.

It’s easy to fuss about actively managed funds’ fees. But sometimes the expertise of a good investment manager can not only protect a portfolio, but even outperform the market. However, few managers have been able to do that consistently, year after year.

Also, diversification is a double-edged sword. It smooths out volatility and lessens risk, sure; but, as is so often the case, reducing the downside also limits the upside. The broad-based basket of stocks in an index fund may be dragged down by some underperformers, compared to a more cherry-picked portfolio in another fund.