Attached Link: http://www.poseworks.com/glowworm/

Multipass rendering (MPR) will help you in three basic ways:

1) Lower-memory renders. Breaking an image into multiple renders lessens the burden on your machine when rendering. Many users have found that they are able to render scenes that previously caused "out of memory" errors, by breaking up the render into multiple passes and then compositing them.

2) Fast changes. If you need to lighten a shadow, adjust a color or tinker with any other aspect of your image, you can make those changes very easily in Photoshop/AfterEffects/Gimp/Whatever, and not re-render. This, more than anything else, is why professionals use MPR--when the boss or the client wants a change made, you don't want to be stuck rendering; you want the fast, full quality feedback that programs like Photoshop and AfterEffects provide.

3) Special effects. MPR makes it simple to add things like glows and depth-of-field to your renders. Particularly with animations, MPR opens up all kinds of new avenues of creativity.

You can view tutorials for GlowWorm and get more info on multipass rendering from the above link.