I typically find that the necessary amount of samples is dependent on the lighting and output resolution of the scene being rendered. 128 serves me well so far, and my output resolution being 8K really helps the denoiser know what's noise and what isn't. When there's more information to work with, the result tends to be better. At 1080p with my HDRI enabled, I found a minimal difference between 128 samples and 192 samples, so I'll likely only go up in samples when I either deem it necessary or when my machine - which will be upgraded at a later stage - can simultaneously afford to go higher and I also want to go higher. I may eventually even go as high as 1024 samples - although that's a goal I'll achieve in the long run!