As I have opined before, scourging is likely to have served as a way to beat down the victim, making it easier to pin her or him to the cross for nailing. I conjecture that viciousness of the scourging would have been tailored to the strength and vitality of the malefactor. A young, strong field slave would merit a horrific flagellation, leaving his back and buttocks in bloody tatters. After the long, exhausting march to the cross, he would be easy to control as the spikes pierced his flesh and bone and fixed him to the wood.
I imagine myself. as soft, undersized and female, to be spared the worst of the flagellum. My understanding is that there were indeed smaller scourges for use on women, and that the female back was spared as being too frail to bear the cuts and tears. I have always imagined that I would receive perhaps six blows across my ass. The barbs and balls on the tails would indeed cut into my flesh, but would leave me able to bear my patibullum all the way to the place of execution.