The cutting portion of the needle will become extremely dull after being used once compared to being unused. A dull needle will cause more unwanted trauma and discomfort for the piercee as opposed to a new unused needle.
Cody Vaughn - APP Outreach Committee
**MORE FROM RYAN BELOW**
Piercing needles are very finely sharpened, they are not designed to be used for more than one puncture. Here are some pictures that illustrate how quickly a beveled needle dulls from use. These are pictures of syringe needles (very similar in design to piercing needles) under magnification after use.