Surveys are used for three main purposes: diagnosing recurring blockages, establishing the condition of drainage before buying a property, and providing evidence for insurance claims or build-over applications.
A proper survey covers every accessible run, not just the one that blocked. It records distances so defects can be located precisely from the surface, and it grades severity so you can prioritise what needs doing now versus what can wait.
You should always receive the footage as well as the report. If a contractor will not hand over the video, treat the report with suspicion.