This is the card that makes Scarlet Witch Scarlet Witch.
If you're playing as Wanda, you have to go with the chaos. Embrace it. This means that you can never fully plan out what's going to happen. You can influence it with Wanda's hero ability to reroll one card. You can also move one number up or down when you have Scarlet Witch's Crest. But you never get full control over everything.
You should always use this when all options are good. When there are minions to hit and schemes to thwart.
But what you REALLY want from this is hitting that +3. Status cards are the most important thing in this game, being able to cancel out entire activations. The best Scarlet Witch decks are usually built around this one card. Scarlet Witch's Crest is a necessity to get out so you can turn a 2-boost to a 3-boost. Then you want to quickly move through your deck with Spiritual Meditations to try to snag these and stun/confuse lock the villain.
This also has an interesting effect where it scales based on the power level of the villains and mods. The more 3-boost cards in the deck, the easier it is to get those status cards.