Thanks for the answers! Agree with Cotty that it could be usefull to have leading blur (due to first curtain sync) to suggest that the movement was backwards.
Donot agree with Christian,also with second curtain sync, blur can be avoided by using highest speed and/or balancing flash and ambient lighting. The reasoning of Tom is in priciple true, but will depend on the camera: if the highest speed with flash sync has some reserve and the minimum delay between the first curtain trigger pulse and the second curtain pulse is sufficient short, the second curtain sync will have the same maximum speed. Agree fully with the example of Steve about getting the decissive moment at night photography. This example triggered me also for the case of stroboflash ( the wellknown examples of jumping ballet dancer, frozen five times during a jump) here first curtain flash is essential!
