Nano V2, U-10 Purpose

Can anyone explain (with confidence) what is the purpose of U-10 as shown in the diagram below? I suspect it may be there to prevent battery current from being used while the USB cable is connected and the Nano is powered on.

it’s a p-channel MOSFET, Which enables Pin-4 to pin-3 when pin-5 is low, and unenable it when pin-5 is high.

Thanks for your sharing.