The  first and second weekends of December are prime time for holiday parties. Everybody in town will be busy. This includes not only your primary contractor, i.e. hotel, restaurant, caterer, but sub- contractors (ie.  rental companies, food purveyors, florists, servers, etc),as well.  Most servers, for example, are independent contractors, with many of them working with several different establishments. When they get booked for those hot dates, it lessens the available pool. You will have someone serving your function, but it’s likely the most seasoned service staff will be booked early. And usually at some point, the top rental companies will close their reservations for the busiest dates.

And here's an important point- a caterer or sales person will be able to give more of their time if you call a month or two early rather than in December.

 So, if you are thinking about a holiday party and want to make sure you receive the attention you deserve, the key word is early.