Nipple piercings make your nipples much more sensitive.  Though it's easy to get infected (mine did - but I want to do it again - if anyone has a needle handy...)

And well, I'm a TS (for those who don't know) and I've got a ring through the end of my boytoy. (Photos on our web site and video store!) And  when I have a sex change I'm looking forward to piercing the new girl toy.

I don't know why.  It's not about pain, because there really isn't much pain with a piercing, just for a sharp moment or if it gets infected.  I guess some people just find it erotic.

Sometimes it's part of bdsm play, a sign of submission.

But unlike a tattoo a piercing can be removed easily if somone's partner isn't into it.  So it never hurts to ask if you are afraid of chipping your teeth.

Giggle,
TS Jamie