temporary tables ?

Hello.
I have some tables that are updated by several users in the same time and
are used in queries for reports. Those tables have rows that are actualy
copied from original tables that are not to be altered. There is a
procedure that inserts rows for every user when connects, along with his
username, so different users can't interfere with each other because every
user has his own copy of rows that he can update, and records are filtered
by current_user.
Well, it's my heritage from MS Access, before I moved to Postgres, because
there is no such thing as temporary table in Access...
Now, I'm wondering is there any true advantage to implement temporary tables
for each user, insted of one table with inserted rows with username for
every user ?
What would be advantage of temporary tables?
Would database grow less if I implement temporary tables (less need for
vacuum ?), in comparison to my current solution with true table with rows
for every user ?

Zlatko