Praise is an expression of recognition and a conferment of status. Recognition and status are important factors in our self esteem and well being. No matter how well paid someone is, if their efforts are never acknowledged the cash will not quite compensate. By the same token, someone who feels recognised and appreciated will cheerfully put up with other inconveniences, including a less desirable income. The most valuable kind of praise is that which the recipient knows to be appropriate. Praise should only be given to the extent that it is deserved.