Most of you don't know this but you have an option of how many threads you can let Blender use.
So, for an example, let's say you have 8 threads. You can let Blender use 6 threads to render and let 2 threads idle.
And then open a new Blender instance and select GPU compute. GPU compute uses GPU for all Blender functions but GPU compute needs few threads to function smoothly. So, with a decent GPU, you can continue working on Blender while you let render on CPU.
Vice versa doesn't work too well because GPU rendering makes everything sluggish.
So, in my case, I use 24 threads when rendering, leaving 4 threads idle. And then I use GPU compute or browse the stupud Internetz.