The Verify that my files are copied correctly option will ensure that the copy of a file is identical to the original file. By default verification is not enabled.

The obvious benefit of enabling verification is that you can be sure that the copy of a file is identical to the original file and is therefore not corrupted. There are many ways in which a file can be corrupted, e.g. memory corruption, data transmission corruption, hardware failure, network problems, etc. In most cases you will not know a file is corrupted unless verification is done.

The drawback to verification is time. Verification can triple a profile's run time. If time is not an issue it is strongly recommended that verification is enabled. You can also reduce time by filtering out what files are verified. For example, you may only want to verify documents, or may not want to verify executable files.

If a copy of a file is not identical to the original then the log file will contain the following error message: The copy is not identical to the original. The original file may have been modified after it was copied. This means the copy is not identical to the original, but it is worth noting that it does not mean the copy is corrupted or invalid. In some cases it may be that the original file was modified between the time it was copied and the time the verification was made. However, corrupted or not, the copy is not the same as the original.

A related option is Make safe copies. By default this option is enabled, and if you are using verification then it is strongly recommended that you also enable this option. This ensures that a corrupted file will never replace the existing copy. 
When this option is ticked SyncBack will copy files in a two stage process: first it will copy the file and use a temporary filename, then it will replace the destination file with the temporary copy (renaming it accordingly) if the copy was a success. This avoids problems where the destination file may be deleted because the original file could not be copied, e.g. because it is locked, or corrupt. With FTP, Safe Copy is actually a three stage process as it must delete the file being replaced before renaming the temporary copy.