While the ESP32 is in deep sleep mode the RTC memory also remains powered on, so we can write a program for the ULP co-processor and store it in the RTC memory to access peripheral devices, internal timers, and internal sensors. In deep sleep mode neither CPU or Wi-Fi activities take place, but the Ultra Low Power (ULP) co-processor can still be powered on. Having your ESP32 in deep sleep mode means cutting with the activities that consume more power while operating, but leave just enough activity to wake up the processor when something interesting happens.

If you put your ESP32 in deep sleep mode, it will reduce the power consumption and your batteries will last longer.