In many aspects of life, complex problems are better solved by breaking down the problem into well-defined smaller problems and solving those smaller problems in a given order. And, even the solution to complex problems that we solved following that decomposition process in the past, might not remain immutable over time.
This is the basic rationale that stands behind the concept of an itinerary.
Any business process can usually be broken down into a set of clearly defined subprocesses. Those subprocesses are usually mapped to specific services or capabilities within an organization (for example, the approval of a specific offer within a purchase order is undertaken by some specific customer care team, the arrangement of the goods shipment is scheduled by the automated delivery system, and so on). All those services have clearly defined duties, and they can carry out their processing in a more or less autonomous/decoupled way. Doesn't it start smelling like...