The best answer to everything, can be found HERE.
Nodraw CAN be used to improve performance. (Faces with nodraw will not be rendered or "drawn".)
Invisble and clip CAN NOT.
Nodraw WILL NOT make leaks when separating the map from the void.
Invisble and clip WILL make leaks. Same as any other translucent texture.
Nodraw WILL still cast shadows.
Other invisible textures WILL NOT.
Nodraw WILL be used to cut VISleaves.
Other invisble textures WILL NOT.
I thought I'd take 5 minutes out of my time to clear some things up.
Don't make leaks in your maps kids!
Edited by Hardcore Bob, 15 August 2011 - 14:51.