Riding in the city, I'm conditioned to almost always have a pair of fingers hovering over the front brake.
I'd like to read the science behind being more responsive otherwise.
I also recall my rider training course - the instruction was to very deliberately keep my fingers wrapped around the grips, not hovering on the controls. The argument was that a rider would have greater stability with both hands firmly on the grips. I also remember my instructor kicking my front wheel back in forth to make that point, demonstrating more stability when holding on. In hind-sight, that is a bit of a stupid lesson to learn. You don't want a death grip on the bars.