The highlights mode on your Nikon D5300 can be helpful. One of the most difficult problems to correct in a photo-editing program is known as blown highlights in some circles and clipped highlights in others.
In plain English, both terms mean that highlights—the brightest areas of the image—are so overexposed that areas that should include a variety of light shades are instead totally white. For example, in a cloud image, pixels that should be light to very light gray become white due to overexposure, resulting in a loss of detail in those clouds.
Highlights display mode alerts you to clipped highlights by blinking the affected pixels on and off. But just because you see the flashing alerts doesn't mean that you should adjust exposure—the decision depends on where the alerts occur and how the rest of the image is exposed. If your subject appears fine and the blinkies are in the background, don't worry about it.
If you adjust exposure to get rid of the blown highlights, your subject will then be overexposed. In other words, sometimes you simply can't avoid a few clipped highlights when the scene includes a broad range of brightness values.
When you shift to Highlights display mode, you see the label Highlights at the bottom of the frame and the file number and total number of files in the upper-right corner. You also see the Protected, Retouch, Rating, and Send to Smart Device symbols, if you used those features.
Like all playback display modes except File Information, Highlights mode is disabled by default.