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The need for add-on modules usually depends on the IT capabilities and skills availability within an organization. Using a module offers a way to take a hot backup of a database even if a site does not have snapshot capabilities. Most of the modules available enable backups directly to the backup server (or tape device) while the application is up. For many organizations, this represents the simplest, most cost-effective way to back up an active database. In addition, these modules often offer an interface that allows easy "point and click" restores which becomes a desirable feature in environments where in depth DBA skills are not readily available. The modules usually take care of tracking and applying the db logs making things even simpler.
Of course, there is always the possibility to create a "dump" or export to disk and subsequently back it up as a normal "flat" file. However, this is a two-step backup (and restore) operation that takes more time and requires up to twice as much disk space. At this point, you are using nearly as much disk as a mirror type copy without the benefits.
In an environment where strong DBA and storage skills are available, I would agree that a snapshot or mirror copy with subsequent backup is probably the best approach and precludes the need for add-on modules. We must keep in mind that these modules provide a means to backup data and that a backup implies a restore before we can access lost data. If designed properly, a snapshot or mirror copy solution can provide almost immediate access to a copy of the data without having to restore it first. Organizations with stringent data protection requirements and proportionate budgets usually opt for this type of solution.
Read Dorian Cougias' answer to this question.
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