In certain areas of the face, a cannula could minimize bruising. Also, in areas where a patient has been operated on previously or injected with other materials on previous occasions, sometimes the cannula meets more resistance, so that's why a needle might be better in some patients, but it varies from patient to patient. They're both good techniques.
Is Injecting Fillers Using a Needle or Cannula More Effective?
Dr. Arthur Handal explains the differences patients can expect when their surgeon chooses to use either a needle or a cannula to inject facial fillers.