The CPU isn't always too slow. For example rendering a spreadsheet, text editor, web browser or CAD screen might prefer GPU to make it visibly smoother and mor

The CPU isn't always too slow. For example rendering a spreadsheet, text editor, web browser or CAD screen might prefer GPU to make it visibly smoother and more satisfying (especially scrolling, compositing and high density text updates), but will still be useful on CPU. And current CPUs are faster than old GPUs for some things, especially if vector instructions are used. And GPUs are sometimes slow due to technical issues such as bus traffic, even if the GPU itself is fast. So it's not as simple as "never use the CPU".