Update: If you want to give it a try, you can start working with Minko 2 beta today!
During last week "Starting With Shaders" workshop, nicoptere asked me about Render To Texture (RTT). RTT is a very common technique used for multi-pass rendering. The principle is quite simple: the pre-passes render the scene in one or more textures. This texture can then be sampled to provide per-pixel data during the rendering pass.
A very common use for RTT is shadow mapping. Shadow mapping is a technique to create projected shadows. The shadow mapping rendering pass will require access to the depth of each pixel as seen from the light source which is "emitting" the shadow. Therefore, each mesh will have more than just a rendering pass. Indeed, we will have to add a pre-pass for each light in the scene to generate it's "depth map".
RTT can also be used to create portals! So it's a very cool feature.