Functional impact is what a medical condition prevents or limits in daily life: work a person can no longer perform, sleep that is interrupted, concentration that fails, activities that now require help or get avoided. Functional impact documentation records those limits in concrete, measurable terms rather than as general statements that a condition exists.

The VA's rating schedule is built around severity, and severity is expressed largely through function. Rating criteria ask how often, how long, how far, and with what effect: degrees of motion, frequency of episodes, the specific tasks a condition interferes with. Documentation written in those terms gives the schedule something to measure. Documentation that stops at the diagnosis leaves severity undocumented, and undocumented severity cannot support the rating the actual condition might warrant.

Good functional impact documentation is specific, honest, and consistent with the rest of the record. It describes limits the clinician observed or measured, in the clinician's own judgment.