Physical and virtual tape drives hold many advantages and disadvantages respectively. Physical tapes receive data that is optimized for a sequential stream and writes in a serial format while virtual tape drives collect data in a random stream and write the data to an arbitrary device. Virtual tapes provide enhances archiving, backup, and disaster recovery. Using a virtual tape drive allows for a significant reduction of risk that physical storage methods have such as device failure or power surge. Virtual tape drives can generally offer higher file fragmentation and performance, however, can cost more due to vendors and licenses.
Physical tape drives are useful when transporting or maintaining backups; their cost also makes them very appealing. With virtual drives, the cost can vary due to how the vendor manages its usage. You might be charged on a $ per GB manner, which can sometimes be more expensive than just buying a sizeable physical drive.