There were a couple of reasons:

It helps clear constraints on a table

"Select into" is quicker then "delete from" or "insert int" for that matter.

Then use SQL DMO to add table...

Before I read the rest of your reply I don't think I was clear enough.  This is all being performed in development.  The first step is to restore production backup...

I have the same question, but am using a "NOT EXIST" functionality.  We are experience tremondous slowness running this query.  Do you have any ideas on how I can increase...