I've heard two different theories for what reading material to seek out when you're deep in the throes of a story you're writing.
1. Read something similar to what you're writing
Burying your nose in a romance novel, for example, can get you in the right mood for your own love story. The problem with this one is that there isn't a perfect way to find a similar book (thus Netflix's famous algorithm competition, for improving their recommendations based on what you've already watched and liked). Should I stay in the same genre? Or go for the writing style I aspire to?
2. Read something completely orthogonal
I think the idea here is that there's too much potential for intersection (Oh no! Crossing of the beams!) between the reading and writing material. For writers inclined toward insecurity and despair, there's no need to compare your writing to someone else's — especially a polished, professionally edited product — while you're in the act of creation. And it might be nice to let your brain relax and wander into other areas.
Anyway, I'm now trying to decide between a nonfiction book about the Anasazi, or a promising fantasy romance. I may end up flipping a coin.