Remotes, whether wired or wireless provide you with the ability to trigger the camera without ever having to touch it. This comes in very handy when doing very close up macro or super telephoto photography where even the slightest camera movement can be magnified many times, resulting in vibration that can destroy sharpness. I have a wired remote I use when doing both of these, it is in essence an electromagnetic "cable release". Wireles, of course, give you a lot more flexibility, but are worthless if your batteries are weak or dead. The wired remotes get their power from the camera itself. As previously mentioned, you can find all kinds of different wired vs. wireless on Fleabay. Nikon's remotes are very expensive compared to the Chinese ones. Do they work any better? Probably not. Does Nikon actually make them? Also, probably not.
Some wired releases also have built in intervalometers in them as well.