Using successfull Push before Knife/Backstab/Blackjack not only increases chances and effectiveness, but you're basically one-round-lagging someone, AND getting your next command in before they do. Generally, unless someone is ready for this tactic and prepared (Not inputting commands unless you miss the push) you are going to catch them trying to put in where/murder/stand etc. and generally not allow them a command until a round after the knife.