Sometimes the gains are huge when you optimize, sometimes it’s like you say. I’ve found it to be rather frustrating to be upping my subdivisions and getting no speed gains. Gotta love that feeling though, when you increase the subdivs on something and it’s like letting a race horse out of the gate…it’s a counterintuitive miracle every time it happens to me. My difficulty is understanding more why and when…love the explanations above.
BTW, today I was rendering this car for an ad; using IBL mostly; test renders were really noisy; time for final - I started optimizing - everything was still pretty noisy no matter what I did. Had the Dome light and GI up to like 700, still too much noise. I was in a hurry with the deadline, so I just scrapped it and used Vlado’s -- saved my butt!!! It took 1.5 hours, but was near perfection - and I got to have lunch with my kids. A good example of why the 1/100 method will continue to be a favorite. Human time is indeed way more valuable than machine time. But it’s a two edged sword, cause sometimes that optimization will save your butt too! I have experienced where the test renderings took longer than my optimized renderings!
Rule of thumb: if you’ve spent half an hour on optimization without seeing major improvements, switch to 1/100, and bring the noise down to around .003-2 - then go live your life and let the machine be a machine.