Two theories: -- If it ain't broke... don't fix it, or -- A periodic health check up is good for photographers AND their cameras
If you are making money with one camera body, and you can have it away for a couple of weeks, sending your Nikon off for a general cleaning and check up may be prudent (I hate that word -- it usually means "politically correct")
Get a sensor cleaning, check up and update of any firm ware.
Now -- if you have several special settings, go into your menu and copy them onto a flash card. Nikon will reset your setting to "factory new" default settings when they work on it and you will have to restore your selected settings, which you can then upload from the flash card! Otherwise you will be in for a session of head scratching and trying to remember how your camera works.
I have two D700 bodies and they are on more or less of a health checkup schedule. I have never had a Nikon fail me in 40+ years, but if your general luck parallels mine, if you have one body and are at a critical money-making juncture, THAT'S when it will go belly up!