I’m putting in a water system right now and thought I would get blinded by science, but then saw the light!
In a drip irrigation system, changing the diameter of the pipe feeding into the drippers can affect the flow out of the drippers, but the impact depends on the specifics of the system:

Constant Pressure System: If the irrigation system is pressureregulated (meaning it maintains a constant pressure regardless of changes in pipe diameter), changing the pipe diameter will have minimal effect on the flow out of the drippers. The drippers are designed to release a fixed amount of water at a given pressure, so as long as that pressure is maintained, the flow should remain consistent.

NonRegulated System: In a system without pressure regulation, changing the pipe diameter can impact the pressure within the system, which in turn can affect the flow rate out of the drippers. If the pipe diameter increases, the pressure drop along the pipe decreases, which can lead to a higher pressure at the drippers, potentially increasing the flow rate out of them. Conversely, decreasing the pipe diameter can increase the pressure drop and reduce the flow rate.
In summary, in a nonregulated system, the pipe diameter can affect the flow out of the drippers, while in a pressureregulated system, the flow should remain consistent despite changes in pipe diameter.
Get blinded by science here…
This is related to Poiseuille’s Law, which describes the flow of a viscous fluid through a cylindrical pipe. Poiseuille’s Law specifically applies to laminar flow and is given by the equation:
According to Poiseuille’s Law, the flow rate ( Q ) is proportional to the fourth power of the pipe’s radius (or diameter, since radius is half the diameter). This means that even a small change in the pipe’s radius (or diameter) can lead to a significant change in the flow rate if the pressure difference is held constant.
In the context of a drip irrigation system:

Nonregulated System: If you increase the pipe diameter, you effectively reduce the resistance to flow, which can increase the flow rate through the drippers if the system pressure remains unchanged. This is directly related to the ( r^4 ) term in Poiseuille’s Law.

PressureRegulated System: If the system is pressureregulated, the flow rate through each dripper is controlled to stay constant despite changes in the pipe diameter. However, the pressure required to maintain that flow rate might change, but the actual flow rate through the drippers would not vary as much as in a nonregulated system.
So, Poiseuille’s Law is very relevant in understanding how changes in pipe diameter can affect the flow rate in nonregulated systems.
The take away answer is
 the most significant change to flow will be the radius of the pipe to the power of 4. For example, change a pipe radius from 2mm to 3mm and your flow Q increases from 2x2x2x2 to 3x3x3x3 or from 8 to 81 times the flow.
 So if you want more flow out of your drippers
 buy bigger diameter drippers (best option to increase flow by the power of 4)
 Increase your water pressure (but that only increases flow by the power of 1]
Your water saver feature on your shower and sink work the same way to save you money by narrowing your pipe and getting less water