One of the advantages of using high-speed sync off-camera flash is for shallow depth of field portraits.
Let’s start with the why. Why would you ever want to shoot in high-speed sync? Well, for starters, we have to understand a little about our cameras and how they work. In order for flash and cameras to work together, they have to be working at the same speed. Think about the light coming from your flash like a car speeding down the highway