I think it’s used, for example, in Discourse Group Sidebar Menus so admins can configure which groups should be able to see each sidebar section, and it is used in Notification Banners to configure the visibility of each banner.
I assumed you’d also use it in your adds component. But it seems that relies on a string of group names instead.
I try to prefer the group type settings, because they help the admin easily enter groups with a dropdown, while they rely on group IDs, which are less likely to change compared to names. And I think it is confusing if the groups list in an object setting and the list type doesn’t work the same way.
For me, writing "everyone" will also result in "trust_level_0" because this doesn't work for visitors is different from the new version, where the dropdown explicitly offers "anonymous_users" - even if I say it won’t work. If saying it in the description was enough, you could have done the same for site settings. For the admin using both types of settings, it will be difficult to understand why, in some places, the groups that won’t work are hidden, and in other places, they are not - not because the component creator didn’t care, but because it’s not yet possible at that place.