Currently Holidays can be configured in 2 locations on Smartsheet. At the administrator portal and at the sheet level. It would be ideal if at the sheet level you could select pull in holidays from your administrative settings. This should be something you can do when creating a new sheet from a template so that you do not have to update your template when holidays progress.
In addition you should be able to select default holidays that 99% of business recognize to auto create Year over Year as holidays in your sheet. Examples include, New Years, Labor Day, Memorial Day, etc. I list here many US holidays because of where I am based, but this would be helpful across all countries.