I mostly read Fantasy books and a little bit of SF, but the main points I would say is better visualization. Reading textbooks gives you understanding, but being able to reconstruct scenes and characters just from a few lines is a nice plus. When reading story from a ticket, it's become much easier to visualize a concrete use case. Also empathy building. Manuals and documentation are very dry and text is more constrained bandwidth-wise than visual interactions. Reading fiction can help you interact better through text emotionally. And we respond better to stories than logical arguments.`
And in general, it also enables you to understand the meaning of some writing for and from others.
Boosting its creativity is a nice bonus.
I like the idea of learning about human psychology though.
I wish there were a lot more non-fiction books dealing with common and uncommon life's situations, which step out of the theory towards what actually happens in practice.