This is what Ziggity has to say:
"Virtually all manufacturers of nipple-type drinkers without catch cups recommend minimum pressure settings for day-old chicks. Most manufacturers recommend settings below 10 cm to start, while Ziggity Systems recommends only 2.5 to 5 cm (1 to 2 inches) of column height pressure in order to ensure dry litter from the very start."
I disagree. Each nipple has a small ball sitting on machined seat, as long as there is no sediment holding the ball open higher pressures make the ball seat better.
Pray tell how?
Because there is greater water pressure behind it. It's like a detent ball with a heavier spring behind it, except unlike a spring once the ball is unseated it is free to move in the water, but it takes a greater amount of force to unseat it to begin with. When the birds are pecking at the line, the entire line vibrates and can cause other nipples to leak a little due to the balls coming unseated. At very low pressures the balls are more likely to come unseated and drip a little.
"Keep water pressure low when chicks are young so that water will flow easily from the nipple when it gets activated by the lightest touch."