ohai

Unless you know with absolute certainty the exact dates of cash flow liability requirement , it would be hard to match the asset-liability flows to leave nothing on the table at all times.

With the focus on keeping the cash available when it is going to be required to meet the spnding requirement, it would be almost impossible to plan ahead for the longer term flows. Hence it would be technically inferior to immuniztion . Keeping cash on hand would lower the net rate of return and lower the duration unnecessarily.

Combo or horizon matching attempts to match cash flow only in the near term when flows are known more precisely , and immunization for longer terms , when the exact opposite it true