When we deliver software products, we need to be able to tell our customers what they're getting. Not only product documentation, but specifically, every time we deliver a new release we need to relay what problems were fixed and what new features were added. If the software is subject to periodic audits, we need to tell them even more, especially the abiltiy to trace a requirement or change request to what was changed.
Traceability doesn't prevent errors and an audit trail does little to help me to recover from one. Does this mean they aren't valuable CM tools? On the contrary, audit trails and traceability are two of our most important CM tools for learning how to mitigate risk.