Physical commodity ETFs generally only exist for products that make sense to store over long periods of time, such as precious metals. However, in combination with a traditional balanced portfolio, commodities can increase risk-adjusted returns over the long term and also help protect against inflation. RELATED: The Foibles of ETF Expense Ratios Commodities are of course cyclical in nature, but they can provide the needed "zig" when the rest of your portfolio is "zagging".