Overview
A product requirements document can create false confidence. A polished document may hide the fact that participants never resolved a critical decision. Document quality cannot compensate for weak alignment.
The destination will evolve. Research, prototypes, implementation, and QA may force a return to earlier decisions. Treating the document as immutable would block useful learning.
There is also little benefit in polishing the journey or destination until it appears perfect. The plan is a hint about where to go. The strongest validation comes from working software and QA, not from another round of wording changes.