FoF is a digger card, a searcher or whatever else you want to call it.
It gives you extra cards which is good, but more specifically it gives you much higher odds or getting very specific cards at the right time. This is why its good but especially shines in decks with some kind of combo that requires components and blue has long been a culprit in the combo game.
Imagine this:
Your getting smacked down by your opponents army of greenies (not the nose kind), and you must get a wrath of god or die. You know you have 4 in your deck but have yet to draw one. Your turn comes, you draw, its not wrath, just some blue thing called Fact or Fiction. You cast it and get to see 5 more cards that regardless of how your opponent spilts them, if one is a wrath your home free.
Imagine this:
Your building a deck to utilize the new threshold ability and you need a way to get the card with threshold in your hand and the rest in the graveyard to activate them. FoF does a nice job of this because it lets you pick the cards you want to cast while dumping the rest making the ones you picked more powerful.
This is a similar tactic I use with my extended Living Death deck. I'm only looking for one maybe two cards and don't mind the rest being dumped because I will get them back if they're creatures. Along with forbid and frantic search, it makes for some nice extended graveyard filling for those nasty recursive style decks such as Living Death or the formally existing Replenish, though its a tad slow for the old replenish decks at times.
On top of this kind of stuff its also slashable because its CC is only 3U and its an instant meaning you can use it at the end of the opponents turn keeping your own resources free for counters and other assorted effects. Its very balanced, the only drawback to it at all if it can even be considered a drawback is that it costs 4 mana where other search and dig cards for blue are often less. Brainstorm is U, Impulse is 1U, Accumulated Knowledge is 1U, Ancestral Recall is U. So its sorta the big uncle of blue searching instants.
And its a good uncle at that.
