The critical point is a point in the creation of the Omega buildings where it is no longer essential to create more buildings, because you already have enough to make it very profitable.
What is the critical point? With experience you can see that between 45 and 50 Omega buildings taken to the maximum height, is a perfect number so that you do not need to expand this type of buildings.
It does not mean that you can not continue to create more Omega buildings, only that it is from that figure, when having the Omega buildings become an interesting source of Neo coins with which to change them for important buildings of energy, water, sewage, etc.. Although this is not the only advantage, because, for example, the task of Neo coins also becomes an immediate task very easy to do.
There are other tricks about Neo/Omega that you can see on the Isla Atlas website.