The thing is that with advanced tech you can cleverly combine sampling strategies so that you actually CAN get this to work in landscape situations.
What TG lacks for vegetation rendering is that it's not utilizing any of the smart tech available nowadays.
Why? Fine detail in vegetation doesn't receive any direct light, while it should. There's a big accuracy issue with TG's object raytracer.
TG casts very few rays for its GI, resulting in ultra-dark shadows without any indirect lighting information in it.
The only solution is to render it at insane resolution so that those few bounces of light TG utilizes actually manage "to get through".
Modern renderers use different methods for improving "resolution" and thus shadow detail looks much more realistic.
The way vegetation "blends" into the scene is so much better. Not to mention how more lifelike the shading looks like.
TG's vegetation looks great as long as the sun is > 90 degrees off camera (basically behind the camera).
This is simply because then there's more direct light and less shadows, which obfuscates the problem with the renderer.
TG's vegetation rendering is slow, has lower visual fidelity and does how many GI rays? 3?? We need a lot more for vegetation!
But yes, you're right in that it's OK for landscapes to have ~3 bounces.
With MIS you can combine sampling methods to reduce variance (noise, simply put) with less samples needed.
With modern tech you can bump that number up without too much performance loss, because the algorithms are more clever and MIS allows you to combine TG's lower fidelity sampling strategies (hence the noisy default water reflections) with the more modern tracing methods like BDPT.
Like this guy and many others....Veach's research on BDPT and MIS, consequently with VCM is what all modern renderers use: Corona, Vray, Arnold and also this guy
So that's why I said it's both very interesting so see something cool, but yet equally painful to realize how much behind TG is and will remain, because advances in the industry are greatly outpacing TG's development.
