Tessellation for example doesn't render more polys, it uses a distortion method in correlation to the texturing to make textured areas appear to have more detailed geometry than they really do.
Err, actually you have that backwards: Tessellation DOES render more polygons. That's the entire point of it. It takes a model with a set number of polygons, and then subdivides it so that it has more polygons than the original model had. Tessellation is pretty much a prime example of what increasing polygon counts on models does.
Yeah, very stupid of me. I was getting ahead of myself when I was typing that up, I meant to list tessellation, and how displacement mapping does nearly the same thing, by using simple eye illusions, and no extra polygons to do so.
Thanks for not being harsh about it. If it were anyone else, I'd be in a full blown argument right now.
The problem with displacement mapping on characters is that the surface extrusion is still dependent on the original polygon area. If a displacement texture looks like it's supposed to extend "out" of the polygon and it's viewed from an angle, it actually cuts off right where the edge of the polygon is, which looks extremely fake and distracting. You can use techniques like parallax occlusion mapping instead which will give proper outlines to displaced surfaces, but it's very difficult to work with when there's lots of little polygons pointing different directions, and it can have some funky results in areas where surfaces should look like they extend from one polygon to the next. Generally you're not going to see anything more advanced than a normal map used on characters or complex models, since most of the other techniques like displacement/parallax mapping is really only good for mostly flat surfaces like walls and the ground.
There's a reason tessellation is the most popular high end graphical effect to apply to existing models: it's about the only one that's relatively compatible and easy to work with that still provides a decent increase in visual quality when it comes to complex geometry. So I definitely wouldn't say that polygon counts DON'T matter, they'll still have some importance to a model's visual representation. In fact ironically almost all of these graphical techniques are focused on transitioning the detail FROM geometry made of a larger number of polygons onto a lower number of polygons. Technically if there was no practical limit on the number of polygons that could be rendered, we would never need to use techniques like displacement mapping or even bump mapping to begin with.
"Walking tanks must exist somewhere for there to be such attention to detail like this in mech sim." - IGN Steel Battalion review