When datapump import job is started with the option TABLE_EXISTS_ACTION there will be some effects on existing tables.
This is default value and leaves the existing table as it is. (unusable if CONTENT parameter is set to DATA_ONLY)
This appends rows to the table and leaves the existing rows as it is.
This deletes existing rows from the table and inserts rows from the source.
This drops the existing table, create it again and insert rows from the source. (unusable if CONTENT parameter is set to DATA_ONLY)
Note: it must be considered about the referential contraints on the affected tables when using TRUNCATE and REPLACE options.