As for the lever effect, reduction of the force required to lift a weight using a pulley
system is always very surprising as it would appear to be a complete violation of
the energy conservation law.

However, this is not at all the case, as the energy required is equal to the force
applied multiplied by the distance travelled (in this case, the length of the cord
pulled). With 4 pulleys, the force is divided by 4, but it will be necessary to pull
a cord 4 times longer to raise the load to the same height.

So that explains where the energy went. As for the weight balance, it should
simply be noted that, in fact, the load is lifted by the tension of the cord, which is
applied 4 times in this example (twice for each pulley suspended, with the strands
of the cord right and left). It is this system which produces the weight reduction
effect.