VO invests in U.S. mid-cap stocks, and its top holdings — names like Howmet Aerospace and Quanta Services — rarely appear in large-cap ETFs. Mid-caps generally carry more growth runway than large caps, but also more volatility.

Its 13.7% one-year return has lagged large-cap ETFs recently, but mid-caps historically go through cycles of outperforming large caps. Adding a modest allocation to VO is a reasonable way to broaden market-cap diversification within a large-cap-heavy portfolio.