The pass-through mapping inserts all source rows. Use the pass-through mapping to load tables when you do not need to keep historical data in the target table. If source rows already exist in the target, truncate or drop the existing target before running the workflow. In the pass-through mapping, all rows are current.
You might use the pass-through mapping to load a fact or dimension table if the table remains static for a period of time, and then changes dramatically.
For example, you might have a vendor dimension table that remains the same for a year. At the end of the year, you reload the table to reflect new vendor contracts and contact information. If this information changes dramatically and you do not want to keep historical information, you can drop the existing dimension table and use the pass-through mapping to reload the entire table. If the information changes only incrementally, you might prefer to update the existing table using the Type 1 Dimension mapping created by the Slowly Changing Dimensions Wizard.