Locked objects (e.g. cannot be deleted or moved if marqueed by mistake) are a great feature when working on a native file, but should be unlocked prior to submitting the file. This also applies to any items which have been set to Non-Printing. If items have been set to Non-Printing on purpose, they should be deleted or the prepress staff should be made aware of items set to Non-Printing. Remember that prepress staff will not have the same level of intimate knowledge about the artwork as the artist, and are literally treating it as another print file, so make sure it is as easy to understand as possible.
Also, the files themselves should remain unlocked (e.g. PDF security) as any edits which may be required will not be able to be made until the password to override the security is entered. Even if a PDF does not require edits, security can also prevent the file being printed or from being interpreted by RIP software which is necessary to prepare plates for commercial printers.
This includes the media that the files are on (e.g. Iomega Zip disks have the ability to be password-protected for the contents to be seen) as well as any compression software which may have been used. If there is a legitimate reason for keeping the file locked, please ensure that the password is available to the prepress operators (even after business hours).