This setting will add a gradient to transparent color for the base fill of the node, which will have an effect to the transparency of the outer radius of the node as well ass to the derived color gradient, as the color to derive from will gradually fade to some degree of transparency. value 100 (default) for this setting means there is no transparency. Value 0 - fully transparent.

Leaving the value to the default will result in the most vibrant gradient. By reducing the value gradient will become more and more grey’ish and transparent.

You can use the transparency to blend nodes into the background, for example.