The most expensive bugs are not the ones QA catches before launch — they are the design decisions that turn out to be wrong after the product has already shipped. Usability testing on a clickable prototype, before any engineering starts, is the cheapest insurance a project can buy.
Prototypes are disposable; code is not
A Figma prototype can be rebuilt in an afternoon after a bad usability session. A production feature built on the wrong flow usually cannot — it has database schemas, API contracts, and edge cases wrapped around it by the time anyone notices users are confused. Testing early moves the cost of being wrong from "expensive" to "cheap."
What we actually test
We are not looking for opinions on color or font choice at this stage — we are watching whether five to seven representative users can complete the core task without help. Where they hesitate, misclick, or ask a clarifying question is exactly where the design needs to change before a single component gets built.
It does not need to be expensive
A useful round of usability testing can run in a week: recruit five to seven participants who match your actual user base, give them three to five realistic tasks, and watch. You will usually see the same one or two problems surface across multiple sessions — those are the ones worth fixing before development starts.