Verify copied files
When this option is enabled, CCC Mobile will calculate a checksum of the files that were copied to the destination at the end of the task and compare those against the source files' checksums. If any files fail this verification, the incident will be reported to you, and the affected files will be removed from the destination. You can run the task again to have CCC Mobile try again to copy the affected files. If you see repeat occurrences of verification failures, though, that could be an indication that the destination device is starting to fail.
Removing files from the source
When Verify copied files is enabled on a Photos backup task, and when all files have been copied and successfully verified on the destination, CCC Mobile will offer an option to remove the files that were copied from the source. This is handy in cases where you're offloading photos from your iPad or iPhone specifically to free space for new stuff.
If any file verification fails, or if an error occurs while copying files, CCC Mobile will not offer to remove files from the source.