the backup will preserve the present state of your registry before the program starts deleting things...this is in case something is deleted that causes problems with your system, so that it can be put back to its prior state in an emergency situation..to be honest, I skip this, as I am pretty confident (OK, read stupidly arrogant if you will) as to what I let Spybot delete, but in your case it sounds like the backup is a good idea from what you've said