Well from my experience, the advantage of a planetary mixer is the speed: the 3rd speed is very fast. I don't have a lot of experience using it for high HR though (I had owned a planetary mixer in my 1st restaurant during 3 years but never did a high hydration dough with it), just a few times a few years back. So I guess this is what it's about.
For regular dough (using low speed), that kind of mixer isn't good if you add oil (in classic/standard dough kneading oil should be added towards the end when when gluten network is already created), as oil will take time to be absorbed (the dough grasps the hook and rubs the oily bowl without actually mixing).
Lastly, I believe that planetary mixers are limited in volume capacity, so for big production, spiral mixers will be the first choices.