I'm interested in power saving also. I don't recall seeing that function discussed in the documentation and the comments in the header file are somewhat cryptic and don't explain exactly what it is for. I would be interested in following this thread to see the answer(s).
What is your current power consumption looking like? I have found that the ble_tracex() function calls will consume a LARGE amount of power. If you have any traces in your code you should put
at the top of your .c files. This will turn your trace calls into no-ops and save power.
In my App I am sampling an ADC quite frequently and do not want to ever enter HIDOFF (deep sleep). But I don't want to disable low power mode completely as that would drive the BLE chip to run at around 6 to 8 mAmps continuously. So I allow "light sleep" in between sampling periods and the chip is currently drawing about 2 to 2.5 mAmps including the ADC which is very low power also.