What's the theory behind using thin spouted kettles when making drip/pour over coffee I own a drip coffee pot:


and one of the other things you can buy is a thin spouted kettle which is used for pouring water one to the grounds.

What is the theory behind this?

Does the rate of water delivery/flow just agitate the suspension of coffee/water in a way that is better?

I also see such items being used in coffee shops too so would really like an expert's summation on this.
By having a thin spout, you can more finely control the flow rate and where the water lands.    When making pour-over coffee, you want to control the water level in the cone to control the brew time and evenly extract coffee.  Also, water needs to be poured carefully onto the middle of the cone so that the water doesn't run down the side of the cone without touching the coffee grounds.