I told someone "No" and they asked why, and I said "'This isn't a strategy game. It's a roleplaying game, and I am the storyteller.'" And they felt that was a lame excuse. Let me show you why I need to be able to make decisions based completely on my conception of story with this example.
I am a mage. I have dex 3, perception 3, firearms 3, weaponsmith 3. I have corr 1, forces 3, prime 2, time 3. It takes twenty successes to craft a single charm bullet. With time 3 and not doing anything else, I can craft, without paradox, an average of three bullets a week. With a final spell of 10 successes, and three points of tass, I can have three bullets that not only do bullet damage, but 7 levels of aggravated damage per hit. Terrifying, eh?
Now, imagine a mage with access to one of the many nodes on the game. I could produce three of these bullets an IC week on average without even breaking a sweat /or/ draining the node. By the end of a year, I could have 156 bullets that do 7 levels of aggravated damage /plus/ normal weapon damage.
This is why I say "no" sometimes--especially when crafting wonders--when it is completely within your ability to do it, /mechanically/. But no mage would spend a whole year crafting nothing but magic bullets. It's ridiculous. It would also make a horrific story. Thus, sometimes when I feel that you are focussing too much on mechanical advantage, or that you are having your character do something that they wouldn't ICly do (your character exists even when you aren't on, and they'd get bored of making bullets), I will simply say no. I hope you agree that I have to be able to do this.