Consider a four-legged chair stood on an uneven floor. The chair rocks a bit. At mid-rock, there is a point at which all the weight is on two diagonally opposite corners, with the legs on the other diagonal clear of the floor.
Many moons ago, an incident occurred at work. A large tank full of cooling coils and other gubbins was being constructed, and for reasons we need not discuss this was happening away from the tank's final resting place, thus necessitating the finished fabrication being moved. To place it on skates, it had to be lifted - 40 tons of it. Some bright spark decided that this would be done by 4 10-ton chain blocks equally spaced round it. The riggers, when they saw the job, were not happy, reportedly; but were told to get on with it. This they did, and despite their best efforts, one chain went a bit slack. This effectively threw 40 tons on to two 10 ton blocks, with the inevitable brown-trouser inducing result - fortunately, without any injuries. After much faffing, it was found that damage was not severe, but - erm - lessons were learned. (NB - happened before my time, so not guilty - but it obviously became a much-related incident.)
Rule is, if you're lifting something at four points, rate each of the four items of lifting equipment at half the item's weight. Thus, for a 1000kg fridge, four bags at 500kg per bag would be wise. Four off at 250kg risks all 1000kg resting on two bags at opposite corners, and the other two doing nothing much. There may be an exception if the 1000kg is flexible enough to evenly distribute it's own weight, but in the case of a fridge, I suspect that's not the case.
Four bags rated to 500kg each, or stay well away.
