Motivation for kids to obey the rules, to play nice or what ever. Parents do this all year long, Santa is just the big Motivator.
I have seen the faces of 3 small little children, with tears in their eyes...who believed in Santa Claus and were perfect in every way but Santa did not reach that year because the parents were too poor to afford presents. They felt they were the ones who did not behave "good enough" to be worthy of Santa Claus showing up to give them a little happiness.
Santa Claus in christmas? A disgrace!