I found the opposite
I stopped Rosetta running because it was incredibly RAM hungry (ca 1GB per core), probably because it seems to run multiple separate processes rather than a single, parallel one like FAH. But even when I had FAH on full throttle on the CPU, not only did it use <1GB in total, it was low enough priority on my system that I barely noticed its resource impact.
However, if I'm running flat out with anything, I have issues with my (stock) CPU cooler (despite significant undervolting), and I've now set FAH to GPU only. This makes much more sense anyway, as I'm on 400,000–500,000 PPD on my (fairly middling) GPU compared to ~20,000 PPD on the (reasonably respectable) CPU. If you've got a GPU that can passably run games from the last few years, then it's GPU all the way.
Biting the hand that feeds IT
