It’s a way to have a collection of people and feeds in one pack - so I could send a newcomer a link and they could click “follow all” - great for communities imo
Discussion
I believe a some clients do this. nostr:npub12vkcxr0luzwp8e673v29eqjhrr7p9vqq8asav85swaepclllj09sylpugg comes to mind!