It seems a good and clean thing to ensure that your deployed files appear on the target system with a consistent time/date. Many Applications seem to do this but other than for care of overwriting Users' existing data I guess it has no real significance. I'm having a purge on my installer packaging and I'd like to know if there any good reasons for specific date/time handling.
Windows Installer uses the timestamp information on files (in some situations) in addition to the REINSTALLMODE property to determine which files should be updated (e.g. "o" means only replace a file if the existing copy is older).
I believe the default behavior is to leave the files timestamped for their original creation (not their installation onto the user's machine). Unless you have a specific reason to do something different, I would follow the default behavior.