You don't have a regular schedule. You left your backup tapes or disks in the same room or location as your computer, and a disaster caused the loss of both. Using an online backup and storage service is not only a good way to perform backups, although it is excellent for that. It's also a handy place to store data you aren't currently using and is taking up space on your hard disk drive that you could use. No more worrying if you remembered to bring everything with you.
Security is probably the biggest concern.
You want to know that no one will be able to read or obtain your data on the Web site. Secure file encryption. Access to every version of a backed-up file. Ability to store both data files and applications. Unlimited number of backups and restores.