This article was initially posted on SQLServerCentral @ 2024-04-26.
Short answer: The column is marked as ‘deleted’ and will stop being visible/usable.
But, most importantly - The record/table size will remain unchanged.
A metadata operation Dropping a column is a metadata/logical operation, not a physical one. This means that the data isn’t removed/overwritten by this action. As Paul Randal mentions here :
“the cost of that will be deferred for the inserters and not for the deleters”.