Dollar BILS are typically useful for companies engaging in asset-liability matching. For example, if a company has a large liability due in six months, the company could invest its cash into dollar BILS now, rather than simply letting the cash sit idle for that time. The effective interest rate the company will receive from holding the dollar BILS will be equal to the return of the specified index during that time period, allowing the company to participate in any gains/losses the index incurs during that time period, but also still guaranteeing that the company will be able to liquidate its position for cash on the date it needs the funds to pay its liability.