It's designed for guys like me who just can't draw for squat. Basically, I can create 3D models of actors and objects, bring them into a scene, define it and have a pretty decent idea of the shots in advance, as well as a basic setup for camera position, with actual camera data. That means I can actually define a camera style, format lens focal length and so on, and set up the shots in actual model space. What that means from a technical standpoint is that any shot I create in the model is one I can actually make, where an artist's rendering may be something that's impossible to recreate.
A side effect of that is that when I'm composing the shot, it won't let me make impossible shots. It forces a measure of practicality on what I want to do.
It has some downsides. The biggest one for me is that there is no lighting ability, and I tend to compose the lights around the camera placement. I think that may be asking too much, as I'd want to be able to model the lights and gels as well. I could likely do something like that in Lightwave or something similar, but there's a huge investment there-- not just in money, but in time spent learning how to use it.
It's also got some limitations in that you have to import object libraries, though you can create your own objects from primitive shapes. In that's it's a kind of analogy for things that might need to be built (such as props and sets), but it impedes my workflow when I want to recreate a particular location instead of a generic building or location-- it would be like having to build a full-size model of my house before I could use it in CAD.
It has some nice film-specific tools, like being able to integrate with scripting tools so the storyboard can be integrated with the script, and the nifty ability to export flash animations. There's also apparently a tweening ability in this last update that I haven't looked at yet, but it looks like a nice way to handle camera moves. It even tweens between model poses.
Yeah, I know, Lightwave.
Another downside: it doesn't have zombies. Or skeletons.