Why a model matters
For a live service entering a new phase, the business analysis team produced a schematic model of all branching logic and information dependencies. That model became the reference for building prototypes accurate enough to test real journeys, not approximations, but full branching with all conditional paths.
Every sub-journey had its own model: pre-task list, trader details, guarantee, house consignments, routes, transport. The prototype was built to match.
The models
The principle
Map before you make. Understand the information architecture and dependencies before opening a design tool. The work that happens before the UI, the landscape mapping, the dependency modelling, is often the most important work on the project and the least visible. Skip it and you will redesign the same screen four times.