Being fairly new, I use however many I need. It is mostly due to render times and not lighting needs. I find rendering figures in Poser and the background in Bryce much faster than trying to render everything in Bryce. I've noticed that the imported images in bryce aren't too clear so I still like to use the Bryce original render. But I think the most I've had so far was 5-6 different renders being only 1 in Poser. But then when I take it into Photoshop or Paint Shop Pro I usually end up with many many more layers.

Macey ^_^