As an example of the importance of low quiescent current this slide shows what happens in the real life case of the STM32L. The power supply required from is 1.8 V to 3.6 V, from 1 µA in standby to tens of mA in the run mode. Where there is a problem is with the 1 µA, because that is lower than the quiescent current of many regulators. The power supply will require more power for itself than it is actually delivering to the load. Hence the importance of low Iq regulators or even better regulators whose efficiency is high even at light load, such as the STLQ015 LDO or L6928 switching regulator.