AIDL is for purpose when you've to go application level communication for data and control sharing, a scenario depicting it can be : An app requires list of all contacts from Contacts app (content part lies here) plus it also wants to show the call's duration and you can also disconnect it from that app (control part lies here).

In Messenger queues you're more IN the application and working on threads and processes to manage the queue having messages so no Outside services interference here.

Messenger is needed if you want to bind a remote service (e.g. running in another process).