The arrow in its parabolic trajectory passes twice through the first pin. The trajectory of the arrow depend on the bow and arrow setup, but it typically starts below the first pin, raise and cross it at around 5 yards, keep going up and make zero again at around 20 meters for example.
Depending on our preference, with the first pin we would cover a “X” distance, but we need to know that it will hit a bit high between the first zero and second one, and low in the other areas of the curve. (Curve is general, it has not been take with my bow).
The important thing is to know our equipment and understand what the arrow is doing. Here a simple test. Start and shoot with your first pin aiming dead center at 5, 10, 15, 20, 25 and 30 yards and check what the arrow is doing. My setup is really quick, I am shooting a PSE OMEN Pro at 70 pounds and 28.5 draw length. The arrows are Carbon Express Maxima Hunter 450 with a total weight of 420 gr, and I am shooting them above 300 feet per second.
My first zero is at 5 yards, and my second one at around 30 yards. Here you can see the grouping (around 3 inches) with just the first pin and arrows shot at 5, 10, 15, 20, 25 and 33 yards (30 meters). I feel comfortable shooting like that with only one pin, I just know that if I want to have even a better grouping I just need to correct a little, since I know how high the arrows are going at 20 yards (peak of trajectory). I love not having to guess the distance under 33 yards, specially for stalkers and quick shots.
This is just and example, since it will depend a lot on you setup, and even with things like the peep height, etc.. Try it for yourself!
Good luck in the woods, be efficient!