MPLS inter AS option A,B and C.. where have you seen this deployed in real life? And why?

I am trying to understand where exactly one might deploy these options. I understand this might be a quick migration option in case of AS mergers but not sure if two separate AS or transit provider would use these options?

If a customer has two locations connected to two separate AS and wants to connect these then they can use L2VPN from one AS and terminate it at the other AS?

Also there would have to business agreement done if two separate AS wants to use these options?