During Christmas, there are few important activities/tours that do not operate. If you are visiting Finnish Lapland and you know you might not be able to come back again, you would not want to miss some important activities.
Well, its usually an individual's choice and circumstances; however, we recommend travellers take a one-way train journey from Helsinki to Rovaniemi or return.
Finland is expensive, and if you are planning for it, you might already know. And, on top of that, you are travelling during Christmas.