There is a direct correlation between the nutrients and in certain proportions to one another can effect phenological traits in cannabis. That means that the type of nutrients given to a plant and how much of each will have an effect on phase shifting from veg to flower, as well as improving yield and quality.
That is why you are given feeding charts and are instructed to use the entire line, not just marketing, but they know if you use the nutes in the right way, you will grow better plants. Waiting for plants to go through the preflower stage before switching their nutes over is nothing new really. Autos are sensitive and require a smoother transition from veg to bloom nutes, that's all really. You can push the strain if you want to push for more yield. It works for sure.