The main reason that most people who say they are pierced, or had their submissive pierced, is as a mark of ownership. Like the collar, piercings have become a visible and constant sign of ownership to those in BDSM. Piercings can be felt, and worn constantly, whereas many collars can not. A piercings can also be more discreet than a collar, so works well as an alternate collar for those who prefer such. Nipple rings, for example, are easily hidden with a bra. Genital piercings are even more easily hidden. yet, the submissive is constantly aware they are there, and frequently reminded they are owned. 

In this way, piercings take on an emotional and mental meaning beyond just body decorations or jewelry. To some dominants, bestowing a piercings on a submissive is an honor that must be earned. It can be viewed as a "step up" from the collar, or a training collar. A more permanent mark of ownership. Such a move, can increase the emotional and mental bond for the submissive. It can bring a whole new dimension to the relationship. For many, recieving a piercing has the same emotional meaning as the recieving of a wedding ring as a permanent symbol of the relationship. In this way, they are similar to a collar.

For others, permanent piercings are a way to enhance the physical characteristics of themselves or their submissives which they find most pleasing. For example a female submissive has wonderful breasts, and the dominant thinks they would look marvelous pierced, as does the submissive. So they have it done. Not necessarily as ownership, but more for aesthetic pleasure. 

Further, for many people, piercings increase sensitivity in the part of they body they are placed in. For some people, it is this increased sensitivity that causes them to seek a piercing (or more than one). 

For some people, it is the added dimension of piercings to the repertoire of play that causes them to have a piercing done. With body piercings there is a whole new way of playing, be it for pleasure, or pain, or both. Many different things can be done with a piercing in place, which give individual sensations, that can not be done without piercings. New kinds of bondage can be introduced into the relationship. A quick way of applying pain discreetly can be added as well. Tweaking a pierced nipple can be more painful than one that is not. 

The reasons for getting a body piercings differ for each person who decides upon one. Like anything else, before doing it, you should do extensive research into the benefits or possible drawbacks to the type of piercings you are interested in. Learn how to care for them, and what to look for in a piercer before having it done. In a BDSM relationship, body piercing should be a mutual decision, either agreed upon at that time, or beforehand when the collar is placed.