Selecting cows with high milking flow rates reduces milking time per pound of milk produced. Time saved per cow multiplied by the number of cows you milk can be sizable if you make 730 milkings each year.
Sims, John A.
"Select Cows With Rapid Milk Flow,"
Iowa Farm Science: Vol. 17
, Article 7.
Available at: https://lib.dr.iastate.edu/farmscience/vol17/iss6/7