@Tyler
Sorry if I missed it somewhere in the thread, but why small cap value over a total market fund? I really like the asset allocation of the Golden Butterfly, but that has me wondering.
I suspect part of it is the underlying mechanics that make this counter-intuitive: what is optimal in a continually-rebalanced portfolio is not the same as in a "buy an X%/Y%/Z% mix of assets and hold/ignore it for the next 3 decades" scenario.
Small-cap-value is more volatile than total stock market in the short to medium term - it has greater dips/bounces any time there's a recession/similar event. While volatility may seem like a negative, when coupled with rebalancing it can become a positive over the long term - you end up buying more of it when the market tanks, and end up getting it cheap before it rebounds.
The argument for including gold in a portfolio is similar - it's highly cyclical(and cyclical in a way that is at least partially decoupled from stocks), and while doing buy-and-hold with a ton of it over the long term isn't a sound strategy, having a small amount of it *and rebalancing continuously* ends up effectively using the volatility to your advantage. Although lots of people tout gold as an inflation hedge, that's not the main reason it works in a portfolio(lots of other assets - including stocks - track with inflation too), it's that it's a cyclical asset that's somewhat decoupled from other assets, and as such it can improve risk-adjusted return if you're diligent about rebalancing.
It's critical to understand that these calculators assume that you are maintaining your asset allocation, which usually means one or both of selling A/buying B to rebalance, or adjusting your ongoing asset purchases to correct for smaller deviations off of your target allocation. If an investor is not doing that and is instead just buying a starting portfolio and holding it, the math changes considerably.
Or to quote the salient part of Tyler's blog post:
But once you start studying real-world portfolio performance and account for things like asset correlations, rebalancing, and the effects of volatility on compound returns, portfolio behavior is way more unintuitive than we naturally think.