The test piece absorbs mistakes that the final piece cannot afford.

Somewhere in a process there has to be a place where mistakes are cheap, and the test piece is it. Its whole job is to be spoiled so the real thing can be attempted with the errors already spent. Skipping it feels like efficiency and is nearly always a way of borrowing risk from later. A ruined sample costs little and the cost is known, which is not true of the finished one.

Before your next piece of work that matters, make a small version nobody will see. Let it be bad, and note which parts went wrong there so the real attempt does not have to discover them.