It's not important. I believe that you as a viewer are more important and how the work makes you feel, but let me elaborate.
In most cases, it's easier to connect for an observer with an artwork through understanding author's history. It can be his upbringing, most significant events of his life, his interests, etc. Mental health often affect the way person perceives the world.
I worked with an artist who has a bipolar disorder, he was interested in reflections, everything that comes in pairs, binary relationships between objects. It doesn't necessary mean that every artist with such a disorder will do, feel, and express themselves exactly the same way. But when he describes his work and interests, you could extrapolate certain things and build on that.
My short answer would be: It can help you deepen your understanding of their work.
PS. Scholars are usually trying to construct a theory explaining how an artist could create something he has never seen before or where is the origin of the work. If you are studying Edvard Munch, his mental health would be addressed to give you an idea, where and how did the author see these images.