I consider giving money for Christmas is not right, unless you donate in a clever way to a needy family. Particularly for young people, it does not seem appropriate. It all has to do with the spirit of Christmas, and money does not fit well into the equation.
I think cash is most appropriate as a gift for someone in need, like a newly married couple that are getting started in a new house. Cash given to someone who doesn't really need it, just indicates that you havent taken the time to think of a good gift.
Yes, there are times when it is inappropriate to give cash as a gift. The primary occasion I can think of is a Christmas gift to a close family member. Giving cash indicates that you have given no thought about to person you are giving the gift to.
Money is an appropriate gift for any celebratory occasion such as birthdays, weddings, and births. Cash or checks should be enclosed in a card and envelope, and may either be mailed or presented in person. However, be cautious of sending cash through the mail, as it may be stolen.