Hi @mike86317 !
What this does is that for classic themes, it will disable the Block Editor for those widgets.
In this case, then, the widgets available will be classic ones.
When the plugin is activated, you will see a screen like this at Appearance → Widgets: https://d.pr/i/cBX9ar
When the plugin is deactivated, you will instead see the Block Editor, at Appearance → Widgets, like this: https://d.pr/i/omEd0y
You can read some more about the difference between Block and Classic themes, here.
Hope this helps!