ITs intended to help assist you to square up to you player and facing him. This allows you to dictate how you wish to guard him, by either shading him to one side towards help, playing close up (he's a shooter) or playing off him (he's a driver/slasher). the function is also useful for off ball play. Using the right stick for putting your hands up help you as well, to where you can play ball denial defense. Id suggest you go onto scrimmage mode and toy around with these functions to get a better feel for them.
The misconception is the function is suppose to stop you your opponent from scoring by getting aggressive with him which is not the case. Throwing their pattern off from the basket or maybe slowing them down but not to completely stop then regardless of their defensive rating.