The Nikon MB-D15 battery grip fits the D7100 and D7200 cameras. Is it worth getting?
The grip basically adds two things: more controls, especially for shooting in vertical mode, and room for an extra battery.
When it comes to another battery, I don’t think I’ll ever need it. The D7200 is rated as something like 1100 shots on one charge. But I guess you may benefit more from that than I will. I only have the insert for using another EN-EL15 battery in the grip. You can also get an insert that takes six AA batteries.
The other benefit, controls for vertical shooting, is more of a reason for me to get the grip. It makes it so much more comfortable and easy to shoot in vertical orientation because your fingers just fall naturally on the controls on the grip, and you avoid that awkward position you can get from shooting vertical without the grip.

And the controls are just as they are on the camera, same look, same clicking feeling etc. That is of course if you buy the Nikon original grip and not one of the many third-party grips that are available. I’ve not tried any of the other ones, but I’m sure they can be great too.
And, of course, we should not shy away from saying that adding the grip makes the camera set up a bit more “professional”. That’s maybe a silly reason, but not one to ignore, I think.
So, is it worth it? It depends on the price and how you’ll use it. For me, it is fixed permanently to the D7200. It adds bulk and weight, but also vertical controls and an overall better-feeling grip of the camera. But I got mine in good used condition for around €35, and if I look around online it sells (new, I guess) for about ten times as much, at least in Sweden. I’m not sure if I would pay that much for it, if it’d be worth it. Even used, on auction sites, it seems to sell for at least €100 right now.