why do some schedules tell you to add veg nutes during a whole cycle?
Because they re-adjust the NPK ratios and allow you to fine tune quite accurately exactly how much NPK to be given at any time.
It's important to understand that the NPK figures are ratio's but they also have a relationship to parts per million as well.
The NPK values on Biobizz Grow and Bloom are -
Grow 8-2-6
Bloom 2-6-3.5
So used together in the same strengths you get 8-8-9.5
If you used Bloom on its own you'd get 2-6-3.5 (1), if you use full Bloom with half strength grow you'd get 6-7-6.5, (2) if you used Bloom with 1/4 strength grow you'd get 4-7-5.5 (3)
So it's easy to see how you can manipulate the NPK ratios by using Grow and Bloom together and because they're 100% organic nutrients they have low NPK ratios on their own but when used together you can boost two NPK nutrients whilst one stays virtually constant. Aka -
Using the formulations as above watch the N figure particularly increase with the changes in ratios used -
(1) 2-6-3.5
(3) 4-7-5.5
(2) 6-7-6.5
In each instance the N figure goes up by 2, Potassium by 2 and 1 and Phosphorus fairly constant. So you can see how easy it is to give the plants a Nitrogen boost in flowering but not really by increasing the Phosphorus ratio. It's a useful technique for advanced growers of fine tuning and tweaking the NPK ratios more to the plants requirements rather than say just shoving a 10-10-10 formulation down their throats.
It doesn't work exactly like this but it's enough to demonstrate the general principle.