Same as the gradient tool. For example if you are applying the Gradient Overlay effect to a layer which only contains one small object far from the image's center, this will scale the gradient to fit within the small object, center it within the object, and link it to the layer so that the gradient moves with the layer. Angle - Drag on the line within the circle to change the direction from which the gradient is applied across the image. You can also drag directly on the image with the cursor to change both angle, and the portion of the gradient that shows within the layer. Scale - This changes the size of the gradient.
Larger settings cause the colored gradations to be wider, and more gradual.
Smaller settings do the reverse. Very small settings cause the gradient to complete within the limits of the image, leaving the end color to fill the remaining area. Using the Preview thumbnail from the Gradient Overlay's dialog box, here are two different Scale settings. First, a scale setting of 62. And, next, a scale setting of 28.