Major changes backed up as they are made. Every three days an automatic incremental backup done to external HD. Every seven days a manual incremental backup done to external HD. Every month a complete backup done to external HD. Every week, and offsite backup done to another HD. Every month incremental backups done to DVD and two copies stored, one onsite and one at remote location. Once per year a complete archive produced before archiving off old data from the live set.
B. Have you ever needed to restore?
Yes, over my career, more times than I care to think about. Often, it's a 'finger trouble' restore required. i.e., when someone accidentally deletes a file. Corrupt files are rare, but do happen. HD failure has happened about three times. Once recent incident was malware. It was easier to wipe the disk and restore os and data to the latest backup rather than try and clean the pest.
C. Have you even thought about it?
Regularly. It'll save us from hd failure, malware, fire, etc.
Backup shold be part of the disaster recovery program and everyone should have a disaster recovery program.
Oh, and yes, I completely agree, check the efficacy of your backups, otherwise, what's the use of doing them.