If I remember correctly, that ESC is an OPTO, meaning it can not power the Rx or servos directly. So you will need either a Rx pack or you will need a BEC. If you want to use a Rx pack, this will do two things. 1. it will give you a separate source of power just in case something happens to your flight pack, but 2. it adds another point of failure.
The BEC you can run off of the flight battery or you can run it off of a separate Rx battery, but it can be much larger for more voltage. If you run it off of your flight pack, and it somehow desolders the main leads from the pack, you will lose your helicopter since you lose power to everything. If you use a separate battery for the BEC, then if the main flight pack loses power for some reason, you will still have control of your servos and you should still have a connection between your Tx and Rx. This will allow you to land with an auto and save a very expensive helicopter.
I myself have never used a separate Rx pack (other than in nitro) and always powered from the main flight pack on everything. Cars/Trucks, planes, helicopters, and multi-rotors. All of them I use the main flight pack. Just make sure you are not over stressing the pack.