I got my nipples pierced back when I was a freshman in college (so 4 years ago).  I took them out 2 years later when I joined the Army ROTC.  I got them re-pierced about a year after that.  I had to take them out for my FFS (not 100% sure why), but when I was actually conscious enough to put them back in like 4 days later, they were closed.  I was thinking about going to a piercer, but decided to let them close permanently.  I will not be getting them re-pierced.  
Now, to get on topic.  The piercing gave my sensitivity a HUGE boost.  HRT, boosted that even more.  I could have like a nipple orgasm.  EPIC!