A prototype is a tool for answering a question. Fidelity should follow that question: a rough flow can test structure, while a detailed state may be needed to test feedback.
Choose a risky assumption.
Build only the relevant flow.
Observe where someone hesitates.
Choose a useful next step.
Explore product behavior through focused interface prototypes. Interface Lab makes navigation, feedback and difficult edge cases tangible while changes are still inexpensive.