Comment by proc0

The difference is if it's hardware accelerated or not, or at least that's my understanding. Software rendering means there is no hardware acceleration. I think the term is outdated because typically it means you don't use the GPU, and this was true like a decade ago and earlier, but I think today CPUs have integrated graphics, so it's like they have tiny GPUs to help render to the screen because it's more efficient. So even if someone is not using a physical GPU, chances are the CPU still uses hardware acceleration, and that's why it works so well today.

I have an Intel i9 with no integrated graphics, if I don't use a GPU, the screen would barely render in very low resolution, although haven't really test it that. I can disable hardware acceleration in the browser and it spikes several CPU cores and is terribly inefficient.