Here's the same scene, but notice now that I've added V4, and another M3 to the group. Computer is still not having any problems. I can even repose three or four of the duplicates, V3, V4 and M3 with no problems. I will give instancing the edge when it comes to crowds and environments, like forests, trees, plants, etc. but frankly, at this point, I can't honestly say it's much better than duplicating.

With Instancing, you have no overhead for the geometry. For instance, that scene has geometry equal to the number of individual figures x their verts, for example. That's a bunch of verts. However, with instancing, those verts aren't "real." Instead, they're just going to be mathematical equations derived from the original geometry. Now, with separate poses and such, there would be more overhead than that. And, if you somehow had different textures on them all, that would take up a big chunk of room and a bit more overhead so the program knew where to put them. But, it'd still be less than "copied" figures.

Instancing isn't good for close-up organic animated stuffs, but is most often used with things that are fairly static. For instance, you could, as was suggested, have a forest filled with thousands of trees. There may be actually only ten different sorts of trees represented by actual geometry, but with instancing, instead of millions of polys, you might have only a few thousand.

Imagine modeling a house, brick by brick... All those bricks would be a lot of geometry. With Instancing, you'd just have to model the one brick. For Poser, there's probably not a lot of use for Instancing. (Some, but not a bunch.) But, for something like Vue, which is often used for landscape shots, Instancing becomes a bit more important.