Just because we are using Datapump does not mean we cannot obey all the rules you have come to rely on for the Oracle Database (such as consistency and recoverability on instance crash).

What happens if the power goes out half way through your import? We can't just say:

"Whoops...sorry about your database, we lost the power and so corrupted a bunch of stuff"

So operations in datapump are protected by undo, so that we can roll them back if something goes wrong.

In terms of TEMP, don't forget that you are probably creating indexes as part of the import. And index creation means sorting the index keys. Sorting = TEMP.

For rare (and large) things like imports, I know clients that will temporarily create a massive TEMP (and potentially UNDO) tablespace (eg TEMP_PUMP and UNDO_PUMP) and use them for the duration of the import, and then resort to the standard smaller tablespaces afterwards.