Where are you getting these ideas from? Don't simply say can or not?

Long exposure noise reduction just takes another shot with the shutter closed so that it can get a black frame.

Every sensor from every camera and every brand, will show hot pixels in long exposures. So the camera takes say a 2 minute exposure, which has hot pixels, then it takes another exposure but with the shutter closed for the same duration (2 minutes), so it gets a black picture with only hot pixels.

The black frame is subtracted from the original picture to get the final picture, clean of hot pixel noise. (The hot pixels appear in the same area.)

So if you turn on Long Exposure Noise Reduction you get a cleaner image without loss in image quality.

If you shoot fireworks though, you may want to turn off Long Exposure NR and make your own black frame shot, and subtract it in Photoshop later to save time while shooting.

ahpingko: Your tripod might not be steady enough, or there is wind, or subject movement (trees for example.)

'd go for the 1st one 
edited : sifu albnok explains above this post 

if you ON the LOng Exposure NR, after u took long exposure shots like 15sec, the camera will take 15sec more then only you can snap another pic.
if you OFF the Long Exp NR, this would not happen.

but you will notice on you picture (OFF Long Exp NR) there will be white dots, IINM called the hotspots or somethinghot pixel. the 15sec after the long exposure is to reduce the hotspots hot pixel . with the Long Exp NR OFF, you see the white dots as if it is noise (iinm).

sorry i dunno how to explain , but sifu albnok had explained before (explained by sifu albnok above me ).

like in this pic.


crop left part of the pic