Every year I seem to think I have the timing of the busy banner season hammered down, and every year it throws me off. It seems logical that November would be the busy season, with clients all preparing for the holidays. Then I would assume December would tail off as everything is already done and prepared and ready for trafficking. 2014 was like that. But this year November was the same as October which was the same as December. 2013 had a dead November, and a killer December.
I guess for freelancers it's not so much about time of year, but more on the particular clients you are working with that year, and their overflow.