Giving my two dimes. I apologise if some else has given it already. And it is quite an operations point of view and mostly based on Oracle. To the best of my knowledge, it applies to Postgres even more.
The data of DB temp tables are not visible outside of the session that has put it in. In the case of trying to find the problem of code of functions storing intermediary results, they are just not visible for the investigator such that one has to do all the steps manually to detect the point where things go wrong. In my opinion a real pita.
