Mastering the Nikon D800 written by fellow Nikonian Darrell Young addresses this topic quite well. I highly recommend his book.
Darrell likes to keep LENR set to ON, unless shooting "action" or "sports" because LENR can effect continuous shooting frame rate. I consider fireworks action so I think his recommendation corroborates the other posts.
His book also covers High ISO NR and its' three settings: Low/Med/High.
I echo, echo helmer and Alan, regarding the value of the Nikonian forum AND add to that Darrell Young's Mastering the Nikon D800, which I found more useful than the orginal manual.