Sorry if this question sound naive. Normally in water pipes, when we see another pipe branch off from a T-junction, that pipe is a thinner one. Say, a 3/4" pipe will branch off only a 1/2" pipe in a T. What is the reason behind using a thinner one?
If water resistance is the concern, isn't that a thicker pipe will always have a lower resistance? Using a thinner pipe only increases the resistance (am I right about resistance Vs size?) If we want higher pressure at the outlet, isn't that only the outlet need to have a smaller hole?
Borrowing the same concept from electricity, there is really no need to reduce the size of the electric wire (except to save cost) if we expect the end point can only consume lower power. We can always use a wire as thick as the main wire anywhere.