Praetor's Grasp combines disruption with access to a useful card from an opponent's library. You search that library, exile one card face down, and may play it for as long as it remains exiled. The card can be a missing resource for your own plan or a key piece you want removed from theirs.
The flexible choice is the main attraction. Against a combo deck, removing an essential card can interfere with its intended sequence. In another game, a mana source, removal spell, or broadly useful artifact may help you more immediately. Looking through the library also gives you information about the remaining deck, helping later decisions even if you do not cast the stolen card right away.
Grasp does not waive mana costs or let you spend mana as though it were any color. You still need to pay the card's cost normally and follow its timing restrictions. A card with demanding colors may be harder to use than a colorless artifact or a land. Playing an exiled land also uses a land play; it is not an extra land drop by itself. Black decks can use Grasp as a specialized tutor when opponents are likely to have useful options. Choose with both halves of the effect in mind: what the opponent loses and what you can realistically use. Taking an impressive spell that your mana base cannot cast may still be valid disruption, but a less dramatic card can sometimes improve your actual position much sooner.
