It allows to address precisely the superficial wrinkles. For example to redraw a contour lips more easily than with a cannula. The main disadvantage is the risk of blue or hematoma since there's always a risk of touching a small surface vessel to each bite.
There are different sizes and shapes of needles. more info here.
The cannula has a blunt end and does not involve any vascular intrusion. It should still make a small hole in the skin to insert, and then we insert it close and close in a dermal plan set to deposit the product injecting regularly and not painful. The risk of blue and hematoma is therefore reduced. Calcium gel is introduced at the level of the oval by a cannula mainly.