what does Camera.targetTexture do?

Questions & Answers
1

What is the destination render texture?

http://unity3d.com/support/documentation/ScriptReference/Camera-targetTexture.html

2

In unity pro you can create a Render Texture and apply it to your camera. Then whatever your camera is able to view will be rendered into the RenderTexture and you can save it as png or use it to make a radar, or simply show a thumbnail of the scene in your GUI.