Drift is a spinner's best weapon and it comes from the seam

The sideways movement in the air that beats good players is a physics effect, not a mystical property of hard spinning.

The ball that beats a set batter in the air, before it has landed and before it has turned, is doing something people describe as magic and which is in fact a fairly ordinary aerodynamic effect.

Drift is lateral movement during flight, and it happens because a spinning ball with its seam held at an angle creates uneven airflow on either side. The side where the surface is moving with the airflow behaves differently from the side moving against it, pressure differs, and the ball migrates sideways. Which means the two things that produce drift are revolutions and seam position, and the second one is the part that gets neglected.

You can spin a ball extremely hard and get no drift at all if the seam is wobbling or presented flat. You can spin it moderately and get a lot if the seam is canted at a consistent angle and stays there through the flight. This is why some spinners who do not turn the ball much are far harder to face than the numbers suggest, and why a bowler can lose drift for a whole spell without losing revolutions, which is a maddening problem to diagnose from the boundary.

The effect on the batter is the interesting bit. Drift into a right hander from an off spinner means the ball arrives closer to the pads than the batter's initial read suggested, which turns a comfortable stride into a cramped one, and a cramped batter cannot get outside the line of a ball that then turns away. The turn gets credited with the wicket. The drift did most of the work.

There is a widely stated view that drift depends heavily on the breeze, and I think that is overstated. A cross breeze helps and every spinner will tell you which end he prefers, but the effect exists in still conditions and indoors, because the airflow that matters is the ball moving through the air rather than the air moving past the ground.

Coaches should measure it. Revolutions get counted now with tracking data, and seam angle at release is measurable too, but I have never seen a spinner discussed in terms of how consistently he holds a seam angle. That, rather than the mystery ball he spent the winter learning, is what separates the ones who beat good players.