Fill flash question
Ok, let me summarize, if I can.
It would seem that the sutter speed and lighting conditions would be the the key for me.
Fast shutter indoors or outdoors and using a flash doesen't matter, front or rear curtain.
Flash and slow shutter speed and low light conditions indoors or outdoors,would be up to me to decide what I want to accomplish. Set the front or rear curtain sync? The subject blur or frozen and where the light streeks are frozen in relation to the subject.