If you only consider returns (and not trading fees or total expense ratios or tracking errors as mentioned by D Stanley below), what would be the difference between a single ETF and several ones matching the composition of that single ETF?
For instance, the Vanguard Total International Stock ETF (VXUS) tracks the FTSE Global All Cap ex US Index and region allocation is 22.20% Emerging Markets today.
On the other hand, the Vanguard FTSE Developed Markets ETF (VEA) tracks the FTSE Developed All Cap ex US Index, and the Vanguard FTSE Emerging Markets ETF (VWO) tracks the FTSE Emerging Markets All Cap China A Inclusion Index.
What would be the difference between investing in VXUS only and investing in 77.80% in VEA and 22.20% in VWO (with let's say, annual rebalancing)?