There are two different kinds of backups: backups for version control, and backups that protect against hardware failure.
Time Machine is version control backup. It protects you from accidentally editing, overwriting, or deleting an important file; with Time machine, you can go back in time, so to speak, and see earlier versions of the file. Versioning backup requires a lot of space, as it spans multiple versions of a file's history.
Time machine does not protect against hard drive failure, in the sense that if you lose a hard drive you can't simply switch over to your Time Machine drive and keep going.
Super Duper, Carbon Copy Cloner, and similar programs are hardware failure backups. They create mirrors of your current hard drive, in a bootable form. If oyur hard drive suddenly ends up deep six on you, you simply boot from the copy and keep right on going, losing only any files that have changed since the last clone.
They do not, however, do version control backup. You don't get multiple snapshots of a file's revision history; you merely get an exact clone of your drive as it was at the moment you made the backup. Using CCC or SuperDuper, you can not revisit a file in previous versions to recover accidentally modified or overwritten versions.
A good backup strategy requires both. This is something I tell my clients; you need both versioning backup and hardware failure backup.
