For Data Warehousing purposes it's nice if source systems use soft deletion for easy detection of deleted rows since a certain point in time. I don't think the use-case is limited to undoing user deletions.

If there is no soft deletion or audit table available, the alternative is to either 1) Select all the source primary keys to find out which no longer exist in the source but do exist in the data warehouse 2) If there is no primary key available, select the whole dateset for full row comparison

Since in corporate settings data warehouses load at least once a day, you can imagine the amounts of data being moved around needlessly.