Exchange-traded funds—commonly referred to as ETFs—are all the rage. While there are several excellent reasons to use an ETF over the seemingly archaic traditional mutual fund, they are not a universally preferable solution.

First, to be fair, let’s review a few reasons why ETFs can be a better solution than mutual funds.

ETFs generally have lower associated costs than comparable mutual funds. This isn’t news, I know, but since costs are one of the few variables over which we have control as investors, I don’t mind flogging this deceased ungulate.

The expense ratio is the most obvious cost reduction. For example, the legendarily inexpensive Vanguard 500 Index Fund has an expense ratio of 0.17 percent, while Vanguard’s S&P 500 ETF has a barely noticeable expense ratio of 0.05 percent. This makes ETFs an ideal choice for investors making a sizable, broadly-based, one-and-done purchase.