The discovery and concept of Hull Speed, lead architects to start designing boats around the racing regulations that specified LWL. As the boats heeled under sail, these long overhangs would result in an effective increase on LWL that allowed the boats to stay within the class while performing as if they were a boat a third longer. Down wind, they remained limited to their measured waterline, but on a reach, a 50 foot boat could sail like a 65 footer.
It also made for some fine visual beauty.
[Edit: what I should have typed was a boat with 50' LWL, sailed like a boat with 65' LWL].