I am faced with having to render parts of an image with area renders and late superimpose them on my main render.

How do I clear the render window to remove the leftovers from previous render attempts so that I can export a clean area render?

This may be a very ignorant question, I apologise. I just don't know how to do this.

Do you mean so that only the last area render you did is the only one visible?

If so, I don't think there's a specific feature for it but I suppose you could always store the camera position, rotate to render under the floor so that you get a black render, then use the stored camera position to get your original view back and render a different area.

That said, I don't really understand why you want to do what you're asking so I'm probably misunderstanding what you're getting at.

You are getting what I want to do!

It is very cool that one can do an area render over your previous render, but the area render leaves a whitish mark on the bottom and right hand side.

I just noticed that there is a "render over black" option in the render settings. I don't know if that would work for area renders but I am going to try it now.

Yes, that did it! Render over black.

Ah, glad to hear it works although that must be a Pro only thing.
Good the hear it exists though, I'm surprised it does!

Nope, that feature goes back to, at least, Poser 7.  I checked my old copy and it is there under Render settings.

I just looked again and almost missed it again, but I see it now, under the dropdown :-P

I used to use area renders all the time. When a scene would crash Poser 8 because it ran out of memory, I'd turn off troubling parts (like transparencies in hair), render the scene, and then just render the part I needed to add.

I still sometimes do it. If I look closely at a render and find a tiny little annoying thing I missed, like a finger digging into some skin or whatever, I just repose and then rerender the hand and layer it over the bigger render in post.

Great for test renders when you only changed a small area, too.

It's an excellent tool.