Instead of birthday and Christmas presents, you get "Brithmas" presents.
If your actual birthday falls before Christmas, you know you won't be getting anything on Christmas day and if it falls after Christmas, you know there won't be any birthday presents.
If your birthday falls ON Christmas... you're boned but at least there won't be a full day of letdown.
2. Brithmas gifts are usually a license for people to kill two birds with one stone while spending only for a single present.