Unfortunately, they can also stray into the street or wrap up their owner with the cord and trip them, especially if greeting another dog. In a veterinary office, retractable leashes can permit dogs to approach each other and cause an occasional disaster as the leashes get tangled. Fights between dogs can escalate because the long leashes make it hard for owners to control them.
Some pet stores ask owners not to bring in dogs on retractable leashes because of their poor control.
I believe a traditional leash gives the owner more control.
(credits to: Lawrence Gerson is a veterinarian and founder of the Point Breeze Veterinary Clinic and a bi-weekly contributor to the Pittsburgh Post-Gazette)