It's a very bad habit and a dangerous one. When you shift to Neutral, the engine effectively decouples with the wheels - this removes the "Engine Braking" action and you have to rely on the main brakes. This makes more wear on the brake pads. If there is going to a skid due to road surface conditions, you don't have any control on the car if you happen to be in the neutral.
Looking at the present generation of drivers on the road, I wonder how many can come out of a skid successfully.
Many would wrongly believe that coasting downhill can save Petrol. This doesn't hold true in modern cars. Maybe older mechanical carburettor types did have some effect, but not now.
You coast downhill, take your foot off the accelerator, the ECU automatically cuts fuel into the injectors. This means that you don't use fuel going downhill while still on gear.
