📦 App Groups
What it is
A shared container (group.com.yourname.app) letting your main app and its extensions — widgets, share extensions, notification service extensions, watch apps — share UserDefaults(suiteName:), files, and Core Data/SQLite stores.
When you need it
Required the moment you ship a widget or any extension that needs your app's data (e.g. a WidgetKit widget showing the user's streak, a share extension writing into the app's database). Not needed for single-target apps.
Setup, review rules & privacy labels — Pro
Per-stack setup instructions, App Review rules, and privacy-label mapping are part of the full reference.