Makes the selected curves (or selected CVs) straighter or exaggerates their existing curvature, depending upon the Scale Factor and Max Curvature values.
Edit Curves > Modify Curves > Scale Curvature > 
Determines how much each segment of the selected curves will be straightened or have their existing curvature exaggerated. The higher the Scale Factor, the greater the effect. The effect will be greater on a curve with many CVs than on a curve with few CVs because the Scale Factor affects each segment.
If Scale Factor is less than 1, the selected curves will become straighter.
If Scale Factor is greater than 1, the selected curves will have their existing curvature exaggerated (by exaggerating the curvature of each segment in the same direction as its existing curvature).
Controls the maximum angle allowed between adjacent segments.
If Max Curvature is 1, then the maximum angle allowed between adjacent segments is 180 degrees. If Max Curvature is 0.5, then the maximum angle allowed between adjacent segments is 90 degrees.
If the selected curve already has adjacent segments with an angle greater than that allowed by the Max Curvature value, and you apply Scale Curvature with a Scale Factor greater than 1 (that is, to exaggerate the curvature of the curve), the curve may actually become straighter. This is because the Max Curvature value is reducing the angle between adjacent segments.