Coats were hung on it in one episode
https://www.thegoldencloset.com/merchant/graphics/00000001/T0460h.jpg
Wayne Enterprises buys and sells companies like Stark Industries

I just saw the episode of All in the Family that served as the backdoor pilot for the Jeffersons, and the railing was in that episode, so it was there from the beginning.

I've always thought the railing was interesting, but don't think it had a practical purpose. As already said, probably to 'separate' the foyer from the living room, but coats were never placed on it.
Also, I don't think it was there the first season, I think it was added sometime in season 2.

New York City apartments in some eras featured sunken living rooms, the living room was a step or two lower than the entrance. See the apartment in The Odd Couple, that building appears to be about the same vintage as the one in The Jeffersons. It makes sense to have a railing around a sunken living room, I believe Odd Couple has one.
My guesses are:

1. The railing is meant to evoke the feel of a sunken living room in an apartment that doesn't have one.
2. The apartment is meant to be a modern renovation in an older building. The renovation leveled the formerly-sunken living room, but kept the railing.
3. The set designer wanted to give the audience the impression of a sunken living room, but decided not to actually build it that way because of the risks and hassles.

Those were trendy in the 70s. It's just a little partition to separate the entry from the living room.

I never noticed it until you pointed it out!
I guess it was as importaint as the door in the kitchen of the Evans' apartment in
Good Times

I just noticed that for the fist time today. My guess is to hang coats over during a party.