The issue with bonds in a portfolio, for me at least, is I own them for a very specific reason: Safety. Especially in unstable deflationary markets. I don't want, nor need, to do speculative activities with my bonds. This is because the time when bonds really outperform other assets is precisely the time when you don't want to have any speculative risk in them (like wide scale credit contraction in the economy bankrupting businesses).
However I think many people get caught up in chasing yield at all costs and forget why it is they own bonds. They start to pretend that bonds are stocks.
But bonds aren't stocks. They have their own unique set of risks: Credit risk and call risk. Two things that you don't want showing up when you are expecting bonds to save the portfolio in a bad economy.
This is why I don't like Non-Treasury bonds. Treasury bonds are unique in that the US Govt. can always print money or raise taxes to pay them off (at least in theory). This means there is very little chance they are going to default compared to non-Treasury bonds. Also there is no call risk which means that if market interest rates fall I don't have to worry about the US Treasury calling back my bonds and forcing me to go out and buy new bonds with a much lower yield (a problem with municipal bonds for instance).
Many of these points I bring up in my
Bond FAQ as well.
Now, if you look at the historical returns of Vanguard's Total Bond Market fund vs. An intermediate Treasury bond fund (which is comparable in duration) you find very little difference in returns:
Vanguard Total Bond (VBMFX) 10 year annualized returns: 6.10%
Vanguard Intermediate Treasury Bond (VFITX) 10 year annualized returns: 6.70%
In fact going back to Simba's spreadsheet from 1972-2009 we get a CAGR:
Total Bond Index: 7.81%
Intermediate Treasuries: 7.89%
So there is no historical return advantage in the total bond market vs. intermediate treasuries.
Next though is how the bonds perform when put under pressure. Here I think that Treasuries show their true power. Being Treasuries everyone knows they are the most liquid and risk free type of fixed income you can own. When the markets panic, guess what people want? Treasuries. They don't want mortgages. They don't want corporate bonds. They don't want Junk bonds. Here are some charts showing this difference:
2008 Total Bond Market vs. Intermediate Treasuries:
2008 Long Term Treasuries vs. many others:
US Treasury Long Term Bonds ETF (Ticker: TLT) in red (up about +35%)
Vanguard Investment Grade Corporate Long Term Bonds (Ticker: VWESX) in dark blue (down about -5%)
Vanguard Treasury Inflation Protected Securities (TIPS) Bonds (Ticker: VIPSX) in light blue (down about -7%)
Vanguard Long Term Tax Exempt (Ticker: VWLTX) in magenta (down about -10%)
Vanguard High Yield Corporate Bond (Ticker: VWEHX) in green (down about -30%)
So there is no advantage to non-Treasury bonds in times of crisis.
Well how about extra returns? Sure I guess this is a possibility but you can lose that extra return in a bad market very quickly. Even if extra returns were a selling point, bonds are a really inefficient way to generate returns vs. just owning more stock exposure. IMO. For taxable investors, it's a really bad idea as the extra yield is largely consumed in a higher tax bill. So no joy there, either.
In the end, Harry Browne was right about bonds. You want to own the highest quality you can with no credit risk. Period. That's US Treasuries for US investors. To me, the Total Bond Market fund owns too many types of bonds I don't want to touch and there are no definitive advantages in the number of bonds it does own vs. Treasuries. There is no advantage in historic returns, no advantage for diversification, no advantage in market crises, etc. In the end, Treasuries are just the better way to go.
EDIT: Corrected CAGR figures for 1972-2009.