I was taught that Xmas was a slovenly commercialist shorthand way of writing, and that Christmas was appropriate for the period...... Of course being rebellious I used Xmas when ever I could get away with it.
Nowadays I have reverted to Christmas exclusively if for no other reason than it recalls the spirit of childhood days in wartime when the only bank holidays were Christmas Day and Boxing Day, and if either fell on a Saturday - tough, because Saturday was considered to be a working day even if most stopped at lunchtime.
In those days it WAS a very short but precious period when families met and held good parties.
Only the Scots had New Year Day and probably lost Boxing Day instead.......... A bit of a change now that last night seems to have been the start of a pretty hedonistic three weeks.
I do confess ........ that relevant data often includes Xmas in the filenames on this computer.