When designing applications where it is necessary to have the lowest possible power consumption, there are several design considerations to take into account.
The microcontroller must spend as little time as possible with the CPU running. The application must stay in a sleep mode as much as possible, wake up quickly to execute a task, and then go back to sleep again.
The three sleep modes, Idle, Standby, and Power-Down, in the AVR DA microcontrollers make it very flexible in designing low-power applications. Also, the Event System enabling inter-peripheral communication makes it possible for the peripherals to trigger actions between each other without involving the CPU. That way, the CPU can continue to stay in a sleep mode using zero power or executing other tasks.
Low-power designs are enabled by taking advantage of the features of the sleep controller as well as the inter-peripheral communication while the CPU is sleeping.