Poser has a render engine? :lol:
It's prolly based solely on programming knowledge of the 80's of last century.

Well, if you look with a debugger what Poser is doing then you may notice that it really recalculates from scratch if changes occur in the material room.
If you move the camera in preview, not mat. room, then it doesn't recalculate everything that has procrdural shaders applied to it. Most of them are not even visible in preview mode.
It only recalculates things that are displayed in preview, e.g. no raytraced reflection.
I have not noticed yet that it recalculates for example a tile pattern applied to some surface that is visible in preview while I move the camera. Ergo I assume it stores such stuff in memory and does only another calculation for render.

Somewhat disappointing is the performance of P7 in material room. With many shaders consisting of 100+ nodes and no or small image maps I experience noticeable delays now that I had not with P6 on a much weaker system in 2005.

To answer the memory question:
Most images require more memory then procedural shaders. For some texture sized 1000 x 1000 you can place many shader nodes. I would say around 25 to 30.