You sign off on your Medical form that all contained in it is true and accurate information.
So this substantiates proof that the extra 400 hours someone might want to claim in the event they "lost" their logbook is correct?
(People who fudge hours should burn in hell.)
An ATO/FOI certifying these hours having actually seen a logbook would provide a much more believable proof in the eyes of CASA, wouldn't you agree?