I think the rope presents a really interesting case study.
When
Virgin Australia transitioned (i.e. stopped being Virgin Blue and upgraded from P.E. aka their "euro-business" style seats at the front), it had to re-educate its guests, all of whom were use to using the nearest toilet (just like anyone who flies Tigerair or Jetstar does), to turn around - a decision presumably designed to add more exclusivity to the front of their aircraft.
So IME Virgin takes Business and Economy separation much more seriously than Qantas, as any interloper in a VA purple boarding queue will know, when they are politely advised to walk back to the red carpet queue. Even the welcome on board as you step over the threshold is different for Business Class. (i.e. "Welcome to Business Class, I/(or the CS's name if an FA is doing BP checks) will be with you shortly"). It persists right up until disembarkation, with a FA moving to position themselves where the rope was (once the doors are disarmed on arrival) to ensure there is no rush forward from Economy passengers into the Business cabin.
Anyway, I agree the rope does its job, in fact so well that IME only two flights stand out where it didn't:
The first was when the rope was broken, or more specifically the magnet (as the CS explained to me) - this meant that after a few Economy passengers started heading forward, she had to spend the rest of the flight standing guard. (Not quite in the same way the FAs do for the pilots on VA, but certainly with one eye out ready to turn people around.)
The second was when an interloper actually detached the rope and used the forward toilet. After the event the CS came over and sincerely apologised that someone had come through and been to the lavatory - so it is obviously drummed into them during training that the forward loo on VA is an exclusive part of the Business Class experience. (Where as on QF they quite obviously take a differing approach for their own reasons.)
I think the rope is also important during the F&B service in J on VA, as the CS delivers everything by hand and really doesn't need the interference from people walking through their work zone. (Noting the CSM on QF does their J service from a trolley, so it forms the barrier.)