What contributes to this streaking? Why doesn't spherical lenses have this effect? How is it used in photography?
Spherical lenses tend to have spherical distortion and reflected light patterns. They are circular and symmetrical.
Anamorphic lenses have a built-in "squeeze ratio" that compresses the horizontal axis of the image during image capture. Unfolding the squeezed image for viewing stretches the distortions or internal reflections, from inside the lens barrel, horizontally. When the angle is right, flare that would be circular becomes a horizontal line parallel to the distorted anamorphic horizontal axis.
Over-saturation of the image sensor can also produce linear picture artifacts. Depending on the "polling" of the chip, the lines can be horizontal or vertical. They can appear white or black according to the type and design of the sensor chip. These tend to be the same width across the entire image unlike your example, here.
EDIT: I don't mean to be flip; but, any effect can be used to advantage if the effect is relevant to the subject or to the image content. Using an effect creatively can heighten the emotion of the shot relative to one without such an image treatment.
I'm curious about the symmetric arrangement of the 5 light spots in a "vee" around the highlight. Fascinating.