When Santa comes to town, people usually start to act crazy and panic, but not Mr. Monk. He shoots him down.
Dead Santa (or his helper, because we never know for sure) always gets your attention and can stir up emotions about the whole Holiday Spirit. Although Santa does not die - Mr. Monk is a fine marksman and shoots him in the right arm - we hear from all the regular characters about their feelings on the whole Christmas 'thing', which is nice.
The plot on the other hand is not as good as one would expect, but shooting Santa in broad daylight keeps the Spirit up, this time of year.
Mr. Monk: "There's no such thing as Santa Claus"