Premonition reveals the next token you're about to draw from the bag. This lets you custom-rig all your modifiers and actions around it.
Got a big action coming up? Play Premonition and-----
-Revealed a 0? Rather then committing everything you have to ensure success enjoy the free success an save your stuff for the next test. This is actually one of the best-case scenarios for Premonition because it will now have netted you a lot of saved resources.
-Revealed an easy to achieve number like -1, -2? Same as above exept a little more costly. You might as well have played an Unexpected Courage rather then Premonition to succeed on this test (or the other skill card equivalents for the upcoming test). Revealing a token you could have accounted for with minimal expense is actually the worst-case scenario, having a high-base statistic to beat as many of the low numbered tokens as possible will synergize with Premonition.
-Revealed a large number like -4, -5? This is where Premonition gets good again, similarly to how Lucky! lets you bridge the gap and beat these hyper-penalties Premonition it this case lets you tailor your expenses to guarantee success.
-Revealed a special icon? In case of scenario specific icons you will now be able to bypass or defend against the token effects whilst still being able to match the numerical penalty. In some cases you might turn the token into an advantage, for example Agnes Baker attacking with Shrivelling to deal 3 points of damage.
-Revealed a token you cannot beat ( for example)? Knowing that you're about to fail you can waste the action on something trivial, get the token out of the way, and attempt the test with a fresh token.
This all will make Premonition seem really really good, but there is a point against it. Whichever use you get out of it from the above you're always spending the Premonition card and this is why it has such a polarizing "good/bad curve", if you reveal a token that still requires you to spend a little cash or a card to succeed (a -2 or -3) then you'll wind up having over-spent to cover a penalty token that you would probably have tried to cover anyway. This all in a faction that typically struggles with card draw (or has some very specific cards that it needs to see) makes it hard to find space for a luxury event like this one.
Two more points: Premonition is free, so it wont weight down an already expensive Spell heavy deck, and it has rather unimpressive icons. A lack of icons means you'll never-ever play it for the icons, playing it to see the token will be better anyway.
Edit: The more I play this the better it gets. A variety of cards synergize greatly. Say you play this early in a round before using Rite of Seeking, you can avert lost actions by doing a different test first or, ifthe token has a decent bonus, you can just draw some cards/gain cash rather then loose the action. Then there's Defiance and Recall the Future that you can deliberately target the drawn token with. If you want to go all the way then you can try tricks like Hypnotic Gaze and try to further manipulate the bag with Olive McBride and the like.