Using kill, you can apparently never be sure. If you stun, you have two options: ramp it up and get victory by having every opponent drop, some unconscious, some dead from an overdose - or keep it down and perhaps fail to stun some. Using vaporize, you have only one option but victory is guaranteed.
The trick of stunning a city block would be unlikely to work the intended way in a society that wasn't playacting Chicago gangsters. Some opponents would be other than burly men in their prime, protected by more than a felt hat, and would be taking cover instead of grandstanding in the open; some bystanders would be wandering the streets instead of doing the classic expected yanking-the-pram-indoors-and-spectating-from-inside-a-stone-building act. You'd either get the partial effect, or then lots of baby corpses.
But we know the standard DSC phasers can do it all - beams and pulses, stun and kill and vaporize. The rifles have not stunned yet AFAIK, though. Can all starship phasers do all the tricks? Or is the stun setting something built into Kirk's hardware, rather than a rarity elsewhere for obvious tactical reasons? I hope we get to revisit that one at some point.
Random phaser (or character?) weirdness: why does Tyler switch to vaporize for his last shot in the simulation? Why does Lorca not kill L'Rell during the jailbreak, but misses and scars her instead? How does somebody not made of nanites resist phasers, either on stun or on kill, let alone on vaporize? Why do people sometimes miss, despite obvious autotargeting in other instances, and why don't these people then compensate by sweeping a beam?
Timo Saloniemi