Bad sectors are a major problem in hard disks, which are found to be mainly logical in nature. Computer companies handle this by usually replacing the hard disk. Most often bad sectors spread and corrupt "Track 0" of the disk due to which it doesn't get formatted, O/S doesn't get installed or copying data gives error. 

Logical bad sectors are irregularities on the magnetic media formed due to extensive read write operations, sudden voltage surges, certain viruses, corruption's in boot records etc.

Main Advantages of Disk Repair

• Makes disk reusable.
• Solves installation problems of operating system.