need vacuum after insert/truncate/insert?

If I insert a bunch of rows, then truncate, then insert a bunch more rows, do I need to vacuum? I've been assuming that TRUNCATE TABLE is a brute-force technique that more-or-less tosses the old table and starts fresh so that no vacuum is necessary.

Second question: Same scenario as above, but now the table has indexes. Is a reindex needed, or are the indexes they "truncated" too?

Thanks,
Craig