You are inviting the smasher to hit at your strength, like the batter who anticipates the ball going somewhere near the plate. You may wait in a neutral stance, like a tennis player receiving serve, and change your grip as you start your stroke, but getting the racket on the smash takes longer. Against a hard smasher you may be forced to wait on your backhand as well as stand deeper in the court. For the smash return, I believe the grip is a matter of preference. I like to hold the racket loosely.
Many players choke up on the handle, which increases maneuverability and racket head quickness.
The return of smash is mostly done with the fingers and wrist. For the backhand, I like to snap my thumb against the back bevel. For the forehand, I hold the racket using a flatter grip, and snap the wrist while quickly squeezing the grip with my fingers. The purpose of the smash return is to return the shuttle is such a way so that the offense cannot smash effectively a second time. If this shot is effective, the defender who executed it follows the shuttle to the net, trying to force the net man to not play the net and lift.