Consistency check is used from time to time for a complete confirmation that there is no corruption in a complete database and also to discover any other corruption.
Corruption in Oracle blocks will appear in database with errors in OS, firmware and hardware or software. Corrupted blocks can only be founded when accessing the table in a database. Hence in the current form the errors are not founded and still they are hidden from being discovered. The negative part is these errors are that they make backup to become unusable. These checks requires a lot of time and the best time to run the checkup is when there is less load or off days.