Firebase cloud functions admin vs root lookups

Getting the hang of Firebase and JavaScript for coding cloud functions; but I guess I'm looking if anyone can explain the pros and cons of using the following for look-ups and/or writes in cloud functions?!

1. the use of admin.database().ref()
   vs
2. root.child()

I myself have been using admin.database.ref() but do I need to!? is it just as good to use the root.child() instead?!

via learningiOS