I think Larian only allow 2 short rests before along rest? So your coffee will be weaker...
Yes you won't be able to get absurd amounts of spell slots, but even 2 short rests is enough to boost your number of spell slots you can use in a single fight. And Bards' Song of Rest ability gives you more short rests between long rests, so by level 12 you'll be able to get 10+ more spell slots per day.
Finally, yes, you can short rest three times before the big boss fight and stock up on sorcery points and low level spell slots. But then again, every party can rest before every fight, if they want to, and that already makes the game trivial. Even a normal sorcerer on higher levels will not blow all his spells on a single boss, so is this even necessary/ beneficial?
That's because players will generally mitigate their spell slot usage before and during hard fights. With the coffeelock, they could theoretically machinegun fireballs with no real drawbacks.
