Does DJI intend the foam gimbal collar to be used during transport in addition to the plastic gimbal lock, or it just for shipping?

It's not needed, gimbal lock only.

Thank you.  I hadn't been using it, but I was second guessing myself.  

I use it just because it's there.

Phantom 3 Pro here, no It's not needed for regular everyday use of the flight kit.
Ah, but if shipping your drone or transporting your drone long distances, particularly in flight, it's smart to use it.

Just more security, for the delicate unit... ;-)

I was going to throw mine out, but I'm glad that I kept it, for those extreme transport modes.


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