I've experienced it once and at Auckland only, in my trip there in 2007. They had this really fierce looking lady (6'+, straight out off WWF) who was asking every passenger to weigh their baggage and she was being extremely strict. I and my wife were together and we had a backpack which weighed around 11 kgs. She forced us to go down to the EK checkin counter get a small bag and transfer the extra 4 kgs to that bag and then only let us pass.

The reasoning given was that it was for "your safety and your fellow passengers "safety" " - they didn't want extra heavy bags to fall out of the O/H bins or people not being able to handle them properly while loading/ unloading their bags if they were too heavy and someone getting hurt. Makes sense - but the manner in which it is conducted made it feel like a going past a military check point.