[whpalmer4]

Yes, you can delete the older backups (who knows, you might even want to purge them from Time Machine, if you use it) that have outlived their usefulness to you. There is no provision for automatic pruning of the backups in OmniFocus at the moment. Use Help->Send Feedback to add your vote for one. Other forum posters have reported using things like Hazel to keep them in check.