In today's market, it's easy to think of holding a bond until maturity under adverse interest rate movements as "not losing money". This is a false model. For example, a ten year treasury purchased at issue in mid-2016 is paying less than the current rate of inflation. When interest rates increase, bond holders lose money. Holding the bond just changes the accounting (and exposure to future swings).
Diversification of bond duration is important in terms of risk management and not just cash flow concerns. Prudent portfolios include equities as well as debt.
While I'm currently in tech, I worked on Wall Street for years (both the trading business and IT).