1. Temp tables are a bad idea, last I knew, because they increase the amount of data in the system tables (every time you create a temp table, you create records for it, it's MVCC, so they don't go away until VACUUMed) and system table bloat has been a serious problem for Redshift, since it seems only to go away on reboot. With a client now, lots of tables, takes 60 seconds to issue a system command. A previous client had to reboot daily. I simply advise clients not to use them.
2. Temp tables do not participate in k-safety, so you avoid that performance cost.
3. I suspect I've seen something odd happening with compression with temp tables. I've not investigated.
4. Using `CREATE TABLE AS` is, for me, verboten. Absolutely forbidden. This is because Redshift selects column encodings, and does a very, very poor job of doing so. Never let Redshift select column encodings (or sort keys, or distribution keys, or rely on auto-vacuum, or auto-analyze, and above all, never use AutoWLM).
