These convos are super interesting to me as a guy building his own poor-man's render farm, and validate some of what I'd heard elsewhere. You do need a huge amount of memory for some scenes, and while the raytracing GPU in my notebook is great for modeling, it doesn't take many 4k/8k textures to run out/crash. I'm not savy enough to work only in GPU and like you say we don't know where a light bounce is headed anyway right. Even with sufficiently small scenes, GPUs and systems to run them are expensive when you can buy 10 year old rackmount servers with 12 cores @ 3GHz and loaded with cheap old memory for less than $200 a pop total. At this point the shipping might cost more than the shipped. I just bought a lot of old servers from a local university for a better deal than that, half junkyard bound they are so ancient.