Let's cut straight to it - there are only two reasons you would need to use high-speed flash sync:
to have an appropriately shallow depth-of-field,
to have a sufficiently high shutter speed to freeze action.
That's it. Just those two things. When you need shallow DoF, or a faster shutter speed than max sync speed, then you go to high-speed flash sync.
What HSS doesn't do - it doesn't allow you to overpower the sun. When you go to from normal flash mode (at or below max sync speed), into high-speed flash sync, then you lose Read more inside...
Going to High-Speed Flash sync, ie, over maximum flash sync speed, comes with a penalty - loss of flash power. This might be a crucial thing when we are shooting in really bright light, and need to match that with flash. So here's a solid recipe for when it makes most sense to go to high-speed flash sync / Auto FP.
High Speed Flash Sync makes most sense when you need either
- shallow depth-of-field, or
- fast shutter speeds,
- you have the flash power to spare.
As mentioned in the tutorial on high-speed flash sync (HSS), there is Read more inside...
using multiple speedlights with high-speed flash sync
This photo of Angelique, our model, was taken at 1/8000 @ f2 @ 100 ISO. Yes, an eight-thousand-th of a second. The accompanying wide aperture (with an ultra-wide angle lens), gives a unique look to the image. The shallow depth-of-field and high shutter speed are mutually dependent effects in shooting in bright light. Working with a fast shutter speed, brought us into high-speed flash sync (HSS) territory.
Do keep in mind that this shoot was more of a technical exercise to work through the settings and see how the flash behaves Read more inside...