Thanks to the built-in flash on your Nikon D7200, you're never without at least a little light. You also have the option to attach a larger, more powerful external flash when scenes call for more light than the built-in flash can produce. Here are a few limitations of the built-in flash:
The maximum flash range is about 28 feet. So don't bother using flash when photographing a stage performance from your seat in the theater balcony — the only things that will be illuminated are the backs of your fellow audience members (who will turn around and glare at you if you keep it up).
Flash range always varies depending on your ISO and f-stop settings. At some combinations, the maximum flash reach is just a few feet. Your camera manual lists the various combinations and how they affect flash reach.
Some exposure modes prevent you from using the built-in flash. Obviously, Auto Flash Off mode is one such mode. But flash is also disabled in these Scene and Effects modes:
Scene modes: Landscape, Sports, Night Landscape, Beach/Snow, Sunset, Dusk/Dawn, Candlelight, Blossom, and Autumn Colors
Effects modes: All modes except Color Sketch
Flash isn't suitable for action photography. Three issues make shooting action with flash difficult:
Burst-mode shooting doesn't work. If flash is enabled when you use either Continuous Release mode, the camera takes one photograph for each press of the shutter button instead of recording a burst of frames.
By default, the top shutter speed you can use with the built-in flash is 1/250 second. The faster the action, the higher the shutter speed you need to freeze the motion. At 1/250 second, a rapidly moving subject may blur.
The flash needs time to recycle between shots. And Murphy's Law being, well, a law, it's pretty much certain that your flash will be recharging when the highlight-reel moment of the day occurs.
If you attach an external flash head, you can use flash in exposure modes that disable the built-in flash, with the exception of Auto Flash Off mode. In addition, your D7200 offers a feature called Auto FP Flash, which is Nikonian for "flash photography at high shutter speeds." For the built-in flash, you can notch the speed up only to 1/320 second, however. If you attach a compatible external flash, Auto FP Flash enables you to access your camera's entire range of shutter speeds.