Zone Defense in the NBA is overstated, first off only maybe a handful of teams even empoy zone defense to begin with and that's for maybe 2 or 3 posessions a quarter to change to tide of the game. Secondly, it's not a true zone as their is a 3 second rule and does not allow you to pack the paint. Good ball movement can beat zone and get you wide open shots with ball movement.
Handchecking allows certain stronger defenders to redirect the offensive player to whichever way the defense allows them to make dribble penetration tougher, and shots more difficult to take. Like what dude posted about the ISO Joe Johnson comment earlier.