[Lizard]

If you need to do a lot of scheduling of other people, or have lots of deadlines and complicated dependencies, you probably do need a project management app. OmniFocus has no way of noticing that you've decided to finish both "Take over the world" and "Cure cancer" for next week and warning you that maybe you need more people or a change of schedule. Or that "Launch new website" is right in the middle of your sysadmin's vacation.

If you want a tool to deal with those kinds of situations, you probably need project management software.