It depends on where you are in the fiction - and that almost sounds like a cop out, but check this out.
So, fiction goes first right? MC establishes some fiction, PC responds with some fiction, some fictional ultraviolence is happening, and then the dice hit the table because the fiction triggered the moves.
We need to consult the fiction to know what kind of die rolls we're talking about. Not just whether its Volatile or whatever, Lashing out or whatever, but so we know target(s).
If you're The Mortal and you're armed with a pipe and three guys are chasing you down a hallway, you may only be able to hit one or maybe two if you describe it right. The MC sets the stakes appropriately, 'okay you're swinging at one, screwing this up is going to give the two others time to surround you' or 'okay you're overreaching to hit two? The last one is kind of circling around waiting for an opportunity to nab you...'
I, personally, unless something has made the Mortal a super-combatant would probably cap it at two and Tell Them The Cost.
Now let's say it's not The Mortal. Let's say it's The Werewolf. Your play group has decided that Wolfmode just makes her more terrifying. She's in Wolfmode. Can probably smack up two guys pretty easily, and it's going after all three that has the chance for something to go awry. But yeah, no. These are three stooges not trained Lycan Hunters. So maybe one Lash out roll, three dead bodies, done.
Or, maybe they're Super Cyborgs from the Big Bad and they don't even care you're a Lycan, one Lash Out Roll affects only one of them.
...until your Werewolf comes in with a bottle of vodka and a burning rag and turns the hallway into happy hour. Sounds like a solid Lash Out against all of the above antagonists. One roll.
...or until the Queen comes in and tells her Gang to get them. Sounds like a solid Lash Out against all of the above antagonists. One roll.
So, all about the situation.
Maybe, at the table, you don't want to play through a days long siege of the Vampire's italian villa but you don't want fiction to glide over it. Ask him how he holds off the other vampire clan and have him roll for it (Volatile or Hold Steady, I guess, up to you). Take that as your cue for the general tide of events and let it all collapse into one moment of montage and then go on with the game.
All about the situation.
Really, a good way of looking at it is that your roll will resolve one thing in fiction it could reasonably resolve. Maybe for The Mortal's bare hands, that Lash Out roll is one goon. Maybe for a Chosen with a sanctified assault rifle, that Lash Out roll is a few goons. If they ever want to stretch the idea of what's reasonable for a monstrous teenager to do -- Tell Them The Cost. Let em have it, but hey, your antagonists aren't standing around picking their noses, man.
Just some of my ideas and how I handle it. :)