When any hard drive sector is marked as dirty bit in windows, the computer will automatically start chkdsk scanning while booting. Their is no specific use of marking a hard drive sector as dirty or bad but I think it is useful if you are having any problem in running chkdsk manually.
- Go to Start and Select Run
- Type CMD and Press OK
- Type command
fsutil dirty set [Drive Letter]
- Doing this will mark the specified partition with a dirty bit.