The business case shows related messages. It can be reached over the left navigation bar. There are two ways of using the business case.

If you switch to the business case from a order, you see all messages that were directly or indirectly created from this one.

If you switch to the business case from another message, you'll see only messages directly related to the selected one.

The business case is only active on message detail pages.

The business case is open till all displayed messages have their final state (finished or sent, respectively). Then the whole business case is finished.