One common thing I see in "lazy" portfolios is a REIT allocation as the first slice to add after stocks / bonds. The theory seems to be that, while REITs are included in total market, they aren't included in proportions that represent the actual weight of real estate in the global economy. By adding a small slice of VNQ or SCHH, for example, you can "counteract" that imbalance.
US investors who invest their equity side in VTSAX but not VTIAX, or at different percentages, are already in theory "tilting". Maybe not as bad as adding a small cap value tilt, but home country bias is an active decision someone makes to invest more in their local economy. This question really isn't for them, as it would be very easy to say "I don't want a REIT slice, so I haven't included one".
But for those who are targeting a VTWAX type scenario (or VTSAX + VTIAX at 50/50 proportions) .... do you have a REIT allocation too? If you don't, aren't you technically under investing in the global real estate market?
I guess the same could be true for not holding slices of commodities, but I think that's a different story. One I know nothing about also
