That means not leaving a logbook at the flight school after you get your PPL. That book is more valuable than the family bible.
Your log book is your personal possession. There is no legislative requirement for the flying school to insist you keep your log book on their premises either before or after you receive your PPL. Certainly bring your log book to the flying school for certification purpose if requested by flying school management or when flying that day - but always take it home afterwards.