I use GPU render engines purely for the fact that they are insanely fast an none of my scenes were a problem with VRAM thus far, which is of course the main drawback of GPU render engines; the limited VRAM.
I used Octane for a couple of years but recently bought Redshift. I am super, super impressed by the speed of it. It practically flew through everything I've thrown at it so far, even with volumetrics, lots of tiny lights, etc.
I don't think any GPU render engine has any special feature that CPU render engines don't have, or at least I haven't heard of it yet. It's more the other way around. I'd say most people use CPU engines because they are more flexible and GPU because they are faster. If you want to render very, very big scenes with tons of geometry and lots and lots of textures you can't just use a GPU render.