What OmniFocus Is
OmniFocus is a place for you to keep all of the stuff you're meaning to do, whether it's the stack of paperwork sitting on your desk that's due now now now, or the marble monolith in your garage you've been meaning to sculpt one of these years.
Of course, you could just make a big list on paper or in an ordinary text editing application. But OmniFocus is carefully crafted to understand task lists: it can show you just what you need to know right now in order to make progress on your many projects. It can remember which projects you are putting off for later, which projects you claim are important but which you haven't touched in weeks, and which projects may blow up if you don't do something about them right away.
The really, really cool thing about OmniFocus is that once you get the hang of it, you can really trust your system and know that nothing is slipping through the cracks. The reward is certainty that you're doing exactly what you need to be doing right now, or even that you don't need to be doing anything at all.