You would fail your driving test in every civilised jurisdiction if you went to neutral at a traffic light and if they are teaching that in HK I'm not at all surprised.
I don't agree. When I first started driving school in 1998, I was told by my (English) AA driving instructor in the UK to put the (manual) car into neutral if I'm more than 2 cars from the traffic light, and to use the handbrake to keep the car at a standstill, but that if I were one of the first two cars in line, to leave it in 1st so I could get moving quicker in case I needed to.
It's been a while since then so I don't remember exactly why he said to do that, but I seem to recall it was mainly for 4 reasons. Firstly, you'd have to wait for the 2 cars in front to move first anyway, and you should always be paying attention to them and the traffic lights as part of general road conditions anyway. Secondly, if you were rear-ended while in gear and while relying only on your footbrake, you might end up hitting the car in front of you - whereas if your handbrake were on then there's little danger of that. Thirdly, having skid marks in such situation might help you with liability. Fourthly, why not allow your left foot a rest? Clutch wear and tear may have been the fifth reason, but let's assume that no longer applies, or never applied, and isn't a concern in relation to autos.
While I'm obviously biased, I also thought he was a very sensible guy who was very conscious of his responsibility to guide the next generation of drivers into good driving and buying/maintenance habits (reining in some of the bad habits I picked up from years of playing racing games), while also being a car fan. He did not just teach me "how to pass the test", but also about things like how to judge traction/understeer/oversteer - with an obvious focus on safety - as well as many driving concepts/tricks which most HK drivers seem to be oblivious of or simply choose to ignore (e.g. how to quickly figure out, without checking your mirrors, how your car is within the lane). He quickly figured out that roundabouts were my weakest link, so we did 2 entire classes on them in Milton Keynes (what a surprise), which I didn't enjoy at the time, but which in hindsight I was extremely grateful for. Then after I passed my driving test first time, during which I probably put the gearbox into neutral at a traffic light, he also took me on the AIM course, in preparation for which he passed me the Police Driver Training Handbook (or whatever it was called at the time) to read, and I had a revelation as I finally got to enjoy some great British B-Roads on the way to and from Stonehenge.
Don't get me wrong, the standard of driving on HK's roads is abysmal, but I think there are valid reasons to put a gearbox in Neutral in certain situations, and it is also far from the biggest "problem" we face as drivers in HK!
https://www.quora.com/When-you-stop-in-a-traffic-light-should-you-leave-it-in-D-or-switch-it-to-N-or-P-with-your-car-automatic-transmission
Should you really shift to neutral when stuck in traffic? | TopGear.com.ph
Topic: Should you stay in gear at Traffic Lights - Driving Test Tips
seem to be consistent with the above understanding/rationale.