In most of the cases you would probably hit the delete button straight away, when you check your pictures and see a blurry image. The main objective of photography is usually to have a clear and crisp subject in focus. However, when used right, a bit of a blur can be quite interesting and give your image a sense of motion.
So how to achieve this effect? When mixing strobe light and ambient light with a slow shutter speed, the strobe will “freeze” part of the subject while the ambient light coming in at slow shutter will create a motion trail before the subject. One of the most common and suitable subjects to photograph with this technique is the juvenile Harlequin Sweetlips due to its nature of moving around constantly.