As a plugin developer & Blender user, I find the active selection to be extremely useful, but, it’s locked behind RobloxScriptSecurity, and is only used a single time in the entire Roblox Studio suite in the Align Tool.
The relevant properties are ActiveInstance, ShowActiveInstanceHighlight and HoverInstance. These properties would just need to be exposed to PluginSecurity.
Examples
Weld Creator Plugin
I have a very old weld creator plugin that creates welds between objects. I’d like this to be a “one-click” button, but instead it has to be relegated to being a widget to select the active object and then hit weld, or to just expect that the user intuitively knows that the active object is the last object selected.
Instance Info Plugin
Similarly to the way that attachments show their info upon hover, it would allow a plugin like this to exist without the need to manually raycast to find HoverInstance.