I've long wanted to learn how to produce concept art.
So I recently decided to put some time in to explore the more advanced features of Affinity Photo. I also decided to learn Blender at the same time, and spent an entire day going through basic 3D modelling courses.
My foray into 3D gave way to a few epiphanies:
The things you can do in 3D software (especially Blender 2.8) are amazing, and worthy of further mastery.
Even though concepts such as vertices/nodes, edges and planes exist when working in 2D (such as with vector objects), working/manipulating them in 3D requires a bit of a shift to your mental model.
Digital sculpting is an interesting creative extension to our ancient visual arts, and can be just as exacting.
Though I may in time become passably proficient with 3D software, I'll never want to be a 3D artist primarily; I prefer 2D more.
3D differs from, but correlates heavily, to the 2D side of things.
On that last point - Rob Chang describes it well:
...That is why so many people recommend learning classical drawing and painting, because doing so will force you to learn the foundations whether you like it or not, and there's no cheating in 2D--either you can or you can't--there are no "polish the turd" buttons like there are in 3D where the surface textures and material properties can be procedurally generated, virtual cameras and lights can be dragged around and positioned, and algorithms can create perfectly rendered scenes for you. In 2D, if you want to create credible and aesthetically compelling images, you would have to actually understand at an advanced level exactly how light and shadows interact and behave on different materials, how forms appear under different lighting scenarios, how local colors interact with the light source's color cast, how the illusion of perspective is created, and so on, and you'll have to be able to convey all of that one pencil line and brushstroke at a time.
Another compelling reason why 3D artists would be smart to learn how to draw and paint, is that the critical foundations of visual art learned in drawing and painting will directly carry over to your 3D, so you're actually learning a universal skill-set/knowledge. Whatever you learn in 2D is just as effective when applied to 3D. The reverse, however, isn't as true. Many things you learn in 3D don't carry over to 2D effectively. In fact, you can be an accomplished 3D artist and still draw and paint like a complete beginner, regardless of how much you understand composition, lighting, colors, anatomy, etc., and it'll take you at least a few years to get up to speed as a 2D artist. But if someone is a proficient 2D artist, he'll be able to translate that same set of foundational knowledge directly into 3D as soon as he learns which buttons to push in 3D software in order to achieve the image he wants.