As with many different things related to my sexuality and the fetish aspects of it, initially I was really against piercings of any kind. It took a couple of years of exposure to the concept of a piercing until I finally found a way how to sexualize it, and find it attractive.
The most consistent (with other parts of this blog and thus my sexuality) reason to like piercings is that it embraces the concept of "suffering for beauty".
Even more so, if a woman gets a piercing because of me, because I want her to have it, then this concept arouses me. She is willing to suffer, even hurt her body to be more like I want her to be. This in turn makes me feel great - because she actually is willing to do this for me, as sign of her devotion, submission and/or love. And in the process of doing so, she will actually start to like the piercing, because I appreciate it so much and love her for what she is doing for me.
The most interesting piercing to me is the tongue piercing. This has multiple aspects. Primarily, it just simply feels so good during tongue kissing or when she performs a blow job. And then secondarily, the pure sight of the piercing in the tongue is an association with her being slutty, modifying her body to please her partner[s] better. Last, but not least, it provides ample opportunity for her to play with it inside her mouth, receiving oral stimulus in return.
Nipple piercings definitely are very erotic, too. They are very decorative, and they also show that the breast is transformed from an organ meant to nurture babies into something else: A body part with primarily decorative and erotic function. So it sort-of symbolizes the very much appreciated transformation from the fertile woman meant to bear children to the female sex toy that I really want. In my world, the only purpose of sexuality is to provide pleasure. Procreation is a problem that needs to be circumvented.