Its a high risk tactic, so Hassling opponent can leave a gap but it can also win you a ball and start a deadly counter-attack. So its up to you, you can untick it anytime....
It is a phenomenal tactic. Loads of goals. Perfect for easy games although it hasn't worked that well for me against better teams. Slowly coming round to the hassle opponents shout. My previous tactics have always been stand off with close down on wingers to avoid conceding from crosses.