Cool, I assume this is B3D?
I'm pretty sure it's his open OpenGL engine.
I was just wondering, does B3D render stuff not remotely visible on the screen (like stuff out of the field of view)?
Depends on your definition of remotely visible. It does cull entities but somtimes they can be considerably out of cameraview and still get rendered. IIRC this is because it uses a frustum sphere to determine whether things need to be rendered or not. Fast, but inaccurate. It's better than nothing.
Anyway, what portals do is hide things that *are* in the field of view but are obscured by other things. It really only suits certain types of games ( first person perspective mainly ) but it's quite effective within those genres.