Windows chkdsk checks the Windows-specific file system info. It does NOT check the drive hardware itself or test the sector read/write capabilities. For a Toshiba drive, SeaTools may find errors that would indicate the drive, while still presently usable, is failing. For example, it may find that several retries are needed to read a sector, or that some sectors are not readable. An unreadable sector is not necessarily a problem unless it contains part of a file you need, especially a Windows system file. If sectors are starting to go bad, more will likely follow and the drive may need to be replaced. It would be better to find out that a drive may be failing sooner rather than later, when it fails to boot or dies completely.