Hi @Globulle. 
A major use case for staged users is the ability to have them email in and receive replies without creating an account.
Check out “whispers”, which allows a group on your site to use “internal” messages that are not shown/sent to users outside the group.
Staged users + whispers are a solid solution for running a ticketing/support system where anyone can email in, let’s your community members discuss it, and then reply with a “regular” message when you are ready to send the staged user a message. 