The term can still be harmful even if a coach shows you what they mean. The problem arises when a student who has been told to "snap the wrist" will turn around an tell others that they must snap their wrist for more power. However, their suggestion will often not be accompanied by the proper instruction. This happen quite a bit -- I've heard it thousands of times from various players for both tennis and badminton. This is where the harm comes in. After a while, "snap the wrist" just becomes a mantra -- a mantra that many do not really understand. Some players that repeat the mantra have the proper mechanics while others who repeat it, do not.