Half the delays are caused by people trying to find a spot for their "hand" luggage!
I agree with ANCDU. I was coming back from BNE-MEL on Friday night, and there was a delay because of people trying to find hand luggage, as well as a seat double/triple booking (I'm not sure which). People were bringing on hand suitcases AND laptops in many cases and it just doesn't work. We were brakes off about 15 minutes late due to this. People were just walking up and down the aisle trying to find space which there wasn't. I don't understand why people don't put things under the seats in front of them if there's no space, especially things like laptop.