It’s very important!
I was going to be a graphic designer and was studying it in college before I got distracted with other things. I believe every great image maker should study design to improve their work. Something as simple as understanding good vs bad Logo’s will drastically improve a photographer’s ability to create a great image with a lasting impression. There’s a certain language you’re taught in design that isn’t necessarily natural to the photographic world and I think that language helps you see certain things in certain ways that’s very beneficial to the final product.