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Archiving is an optional feature; nothing requires you to use the command.

Why not just delete stuff as you complete it? Or, if you don't want to delete items immediately, collect them in the archive and then just periodically delete them from there.

Having said that, it might not be a bad idea for the option of archiving or deleting old actions using the same mechanism. You should send feedback to Omni to make a feature request (go to Help -> Send Feedback in OmniFocus).