For all the technique and execution that can be honed via punching, kicking, or otherwise striking at air, it’s difficult to attain true practical mastery of any striking martial art without actually making contact with something solid.
After all, would the All-Pro lineman who never hits a blocking sled or clean-up hitter who never sees the inside of a batting cage please step forward? Anyone?
Shadowboxing may develop execution and speed, but only hitting an actual surface that provides some resistance ties power to technique. With that in mind, every Wing Chun kung fu student worth his or her salt ought to own at least one set of sand punching pads.