In the Preferences window
 

there is a Convenience checkbox to "Remember source & destination volumes" .

What does that do ?

Thanks

It remembers the source and destination volumes in the default settings.

Meaning the "Copy" & the "to" fields in the SuperDuper window would be automatically filled in I assume.

Thanks

If you had previous selections, yes. If not, of course, no. (The default is checked, FYI.)