VXF holds U.S. mid- and small-cap stocks not included in the S&P 500. Top holdings like Snowflake, Cloudflare, and SpaceX give it a completely different composition from large-cap ETFs.

Combining VOO (large-cap) with VXF (mid/small-cap) can replicate the effect of VTI (total market) while letting you fine-tune the exact split — useful for investors who want more precise control. If you already hold VTI, though, there's no need to add VXF separately.