Flash to „freeze“ moving Subjects
The third typical shooting situation is a bit more specific and less frequent.
It uses the fact that the flash sends a burst of light for only a very short time in the range of 1/1000 s for a strong flash, a fraction of it if you do not use its full power or have small ones.
This can be a good mean to freeze moving subjects or to get at least a sharp image that stands out from blurred motion around. As an example see here the rotor lighted by the flash, captured sharply within a disc that comes from its fast rotation during the rest of the exposure time.
The ratio of this sharp image lightened by the flash and the blurred rest is depending on the quantity of ambient light and your settings for aperture and exposure time.