I have mostly Stable Value, Total Bond, Pimco Total Return, and Intermediate Treasuries. Each fund has a particular role to play in our 401k/Roth portfolio-- at least, that's the idea! When I first reorganized my funds, away from high expense investments, I sort of walked down the bond fund buffet line, and put a little bit of everything on my plate. But at my last reorganization this year, I asked myself to justify each fund, and not everything made the cut. Here's my reasoning:
The Stable Value does not fluctuate, and helps with the sleep at night factor. I used to hate it-- I was more or less forced to own it because that's the way the 401k is structured, and it does not pay very well. But I have grown to appreciate it's lack of drama. No matter how crazy Mr. Market feels, I get that periodic $18.41 in SV. Not much, but it's reliable and slowly growing.
Total Bond gives decent diversification, obviously. PTTRX gives even more diversification, and includes several categories of bonds that TB does not have. I think they work well together, and I'm certain Bill Gross is acutely aware of Total Bond. I'm a little concerned with the use of derivatives in PTTRX, but yet not so concerned that I'm willing to get out, because it does do well, with a remarkably low SD for a riskier bond fund. I use PTTRX to raise the return on the FI side, to lose a little less to inflation.
The pure Treasury fund is crash protection, a flight-to-quality "insurance policy." People are dissing Treasuries right now, because they don't pay a good income, but I won't be looking for income until we retire. Despite that, I see the Treasury fund working for me on bad days in the stock market-- it doesn't make money, it keeps me from losing money. That's something I got from reading Charlie Ellis and watching Ichiro Suzuki, the baseball player. For me investing is not about trying to hit one out of the park, I work on (metaphorically) good defense, fewer errors, and (hopefully) lots of singles.