What is the use case for UNLOGGED tables

I am trying to understand the use case for UNLOGGED tables in PG. I am specifically talking about normal tables which
needto be turned into UNLOGGED for a specific purpose like bulk loading because generating WAL logs during the load
makesno sense, even when we take into consideration that this generally breaks replication.  
Typically work flow is:

1. Turn off logging on the table.
2. Load a large set of data using some bulk load tool.
3. Turn back logging.

Depending on RDBMS, some make (3) less painful and some make it painful by rebuilding all indexes.  DB2 is very good in
thatas the only 
penalty you have is in step (2) when the table is locked exclusively.

With PG step (3) basically rebuilds entire table.  Imagine a 500 million row table, which got additional 30 million
rowsvia a batch load. Does PG 
rebuild entire 530 million rows ?  Then what exactly is the benefit of UNLOGGED tables, unless we have permanent
unloggedtables for disposable 
data.

thanks.