In Poser Pro 2010, if a whole character or prop is invisible, it doesn't seem like Poser loads their textures into the calculations when rendering the first time - which could speed up the initial render. But, if you had any part of their body showing, I think Poser calculates their entire texture collection.

Back in the Poser 5 era, I could have sworn Stewer did mention that making elements invisible that were out of the camera's view did help lighten rendering processes.