DMT measures the average duration of a liability (Defined Benefit Obligation or DBO liability in this case). Liabilities with higher duration have a higher discounted value and are thus more sensitive to movements in discount rate, and vice-versa.
In a wider context, DMT is also used as an investment risk management tool. Investment managers and/or actuaries may match the duration of assets with duration of liabilities calculated using DMT. This is a part of minimizing interest rate risk strategy, also known as “immunization strategy”.