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