A system of removable cartridges can become unwieldy and inconvenient if the size of the media is so small that each backup requires multiple cartridges. For some users, this isn't a problem, but for others, it can be critical. Another drawback to a long backup process is that it might encourage the user to postpone or avoid the task. An ideal backup system involves storing duplicates off-site. Sometimes different computers will have data that needs to be synchronized.
Encryption is one possible solution, but there's an associated cost of convenience.
Many users have belatedly discovered their backups were all invected with a virus, for instance, backed up automatically by the system. Currently there are solutions like tape drives, which use inexpensive magnetic tapes and hold many gigabytes of data, but are slow, prone to error, and expensive. Some people use Zip disks or a CD-ROM burner to backup critical data. Neither has the capacity to back up an entire hard drive at once, however. That's ideal backup as it's offsite and therefore secure from physical damage to your computer.