[xivzgrev]

Anything. Vanguard index funds just track the market so there's no hedging.

The main planning I could see overlap is executing large trades since they're both moving massive amounts of money.

[baking]

You are only moving massive amounts of money if you are moving massive amounts of money. Having massive amounts of money invested in ETF's doesn't mean you are executing massive trades if you are holding endowments and your only trades occur when you invest new gifts, withdraw a constant income stream, and rebalance your portfolio mix on a regular basis.

[aninhumer]

Surely Vanguard still need to make large trades whenever the make-up of the indices change?

When the (e.g.) 500th and 501st largest companies swap places, don't they need to sell one and buy the other to keep tracking a 500 share index?

[jonknee]

Yes, rebalancing days involve some volatility.

The way these index ETFs work though is that broker dealers can trade a basket of securities matching the index for a share of the ETF (and vice versa). Because of this price mismatches get fixed very quickly. S&P announces also changes ahead of time so while there is initial price movement it's not all instantaneous.

[baking]

The funds in the OP were Total Market Funds, not index funds.