i think it's more of an etiquette (which is why Western says that). i think IMMEDIATELY after your interview, interviewers have like say 5-10 minutes where they write their evaluation (UCSF emphasizes to say why people may be last and or have to wait). those evaluations will be turned in w/ your profile.
from then on, the interviewers can't write anything else (unless they are on the committee). the committee then review your ENTIRE paper application again + w/ the new evaluations (of both interview & writing) and make final decisions.
i think schools suggest that b/c it's a nice etiquette to do. but i mean it's not gonna affect their decsion to admit you or not.