You can by more bonds that may be priced inefficiently like MBS and munis. If your "client" had a bit more money they can get munis in a separate account structure. Buying munis in a separate account decreases the pain of shifting whims of the retail mutual fund base and an adept manager can find a lot of value in munis due to their inefficient trading. Those are just two ways to get a little bit yield in the bond portfolio for people with a need for a high allocation to fixed income.