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.
If we were talking about deleting data (records), as Paul Randal mentions here :