select into is faster because it is a minimally logged operation.
It only logs the fact that pages was allocated but not the data
oic, so direct copy table by "select into" can speed up processing & reduce trx log . but according to sql server manual, it's not recommend us to "select into" bcos it may lock tempdb system tables in long processing query
any general guideline? e.g in term of output data size or processing time.