The normal use for the platform was for passengers changing from Up Overland to Down Inter-Capital Daylight. Not uncommon for late running to complicate things back in those days.
One memorable use was when 4472 had newly arrived; a special day-return trip was run to Albury and due to lack of paths into Spencer Street, we boarded at Sunshine on the Down. We were able to run all the way in on the Up trip, although some still alighted there. The only time I ever used that platform; none of us bothered to take the photo, which I guess proves that you really should record everything.
From memory, it was constructed in time for the 1962 opening of the sg. Dunno when it fell into disuse, maybe when they replaced the ICD with XPT?
(4472 being the steam version; imaging the hardships they would face trying to run it these days? Still, maybe we could impose "grandfather rights"!)