tl;dr Well Prepared, Archaic Glyphs (Guiding Stones), The Necronomicon is a crazy combo that can trivialize clue-gathering.
In longer form...
This card is a core piece of my favorite Arkham LCG deck: Joe "The Book" Diamond. It's a basic three-card combo deck that can perform absolutely mind-boggling feats of clue-gathering and save tons of actions.
So we've got the Nomnomicon. What's the rest of this combo? It's pretty simple, but at the time of writing only Joe can pull it off. You just need Archaic Glyphs and Well Prepared! With the Necronomicon this comes out to 15 XP total. Triggering Well Prepared on the Necronomicon gives you +5 to Intellect, which with nothing else is already a 9-value stat. Assets and other commits, as well as skill boosts from the Necronomicon, can easily raise you enough to pick up 3 or more clues reliably per action.
Plus, this card just straight value in Joe. It supplements free clues from his Hunch deck, damage against enemies, and can be refilled/used for free via Truth from Fiction, Astounding Revelation (if you're running searches), and Knowledge is Power.
You won't always need to spend four Nomnomicon charges, exhaust two copies of Well Prepared, and commit four Intellect icons from hand in order to succeed an Archaic Glyphs investigation by 23 and pull 12 clues off of a single location with a single action. But when you do, the Well Guided Necronomicon is here to help!