Does one need to drop / truncate objects before importing

Before one import rows into already populated tables, one needs to truncate or drop these tables to get rid of the old data. If not, the new data will be appended to the existing tables.

One must always DROP existing sequences before re – importing. 

If the sequences are not dropped, they will generate numbers inconsistent with the rest of the database.

Note: It is also advisable to drop indexes before importing to speed up the import process. Indexes can easily be recreated after the data was successfully imported.