Sometimes a police stand-off with a knife-man goes on for a long time, such as today's 40 minute wait until the police fired.
"Shooting too few tranquiliser darts would result in partial effects only, while too many can kill the target. According to James Butts, former Chief of Police of Santa Monica, "Tranquilizing agents don't affect everyone uniformly. Therefore you cannot predict whether or not you have a sufficient dose to tranquilize the individual. Second, any tranquillizer will take time to enter the bloodstream and sedate the individual. If someone is advancing on you with a deadly weapon or a threatening object, there's no way a tranquillizer would take effect in the two to three seconds it would take someone to seriously injure you."
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The risk of too much is the same risk as a bullet in the chest. If he has a knife the man can't shoot back and the dart will have some effect in slowing him . The benefit is the greater chance of darts not killing him as bullets do.

So?

nicknamenick,

Maybe 1 mark out of 10. But only because you didn't suggest a Phaser (Star Trek) set on stun.

"So?"
A bullet breaks things like bone, brains and false teeth. A dart does not break things. A guy on drugs with a knife does not really need to die. Death is so....final.
The Phaser has a magnet but obviously won't grab a knife will it?

If someone on drugs (guy or doll) attacks me with a knife then they are going to die or be seriously injured. Let's forget all the BS other methods of resolve, a bullet, for those who are privileged to have that resource, is the best and safest answer.

In the example the standoff was for 40 minutes. No one was damaged at all apart from a slug of hot lead ripping into the guy's panels and chassis costing how much in surgery and spray paint? So a dart is good for everyone and the guy slowly sinks to his knees begging forgiveness.