Before you go deleting millions of records DON’T! You need to watch this video to understand why you should not delete records in one full swoop but rather in blocks.
Inserting millions of rows will take a tow on the transaction log. When you’re inserting this much data, your log file will quickly grow and will have potentials to crash your database. To help relieve the pressure of the log file, you’ll want to insert in batches (this is something that is done in SSIS).