I haven't used SuperDuper. It sounds like it does the same think or closely what Time Machine does. Why would it be needed over or instead of Time Machine?
I'm sure there's a good reason, i just don't know what it is since I don't use it. I'm a big believer in backups, so I'd love to know.
Cheers
Although both are backup solutions, SD & TM are completely different. TM captures a baseline, then incremental snapshots of the changes that can be restored discretely for any point in time that TM has been active. SD, on the other hand, maintains a periodic updating clone, that is, you have a perfect copy of the entire environment as of the latest update.
TM allows for restoration of individual files, apps, emails, etc, that have been deleted months earlier, while SD is what you have now. For example, if I delete an email today, SD's backup tomorrow morning will also have that email deleted from it, whereas TM will allow me to recover the email in a few months if I suddenly need it again.