Created attachment 164662 [details]
Glow and Shadow Sidebar
The glow (and soft edge) sidebar have Radius: and the widget activated if the Radius was more than 0 pt, the widget is active.
The shadow widget has an Enable checkbox and than you can change the Distance. I suggest to remove the Enable checkbox and if the Distance was more than 0 pt the widget was active. So shadow group will have the same behavior than glow and soft edge.
con: the default distance is 6 px if you remove the enable checkbox the default distance is 0 px and the user has no "good" default distance. From my point of view 6 px is a to large default distance.
Would prefer a clean sidebar with at max the checkbox to enable the feature (and fine-tuning in dialogs). But for sake of consistency it would be an improvement to change as requested.