Critical.

 (Note that documentation can be electronic, not necessarily paper.)
•    QA practices should be documented such that they are repeatable.
•    Specifications, designs, business rules, inspection reports, configurations, code changes, test plans, test cases, bug reports, user manuals, etc. should all be documented.
•    There should ideally be a system for easily finding and obtaining documents and determining what documentation will have a particular piece of information.
•    Change management for documentation should be used if possible.