In a way, yes. My day job as a tech writer requires juggling multiple non-fiction projects on a daily basis (well, at least I promise my boss they're non-fiction
), and in the evenings and on weekends, I work on my novel.
Yes, it's different parts of the brain, but yes, brain space for both can be a major challenge. That's probably actually been my biggest challenge ever since getting into tech writing: the job requires creativity with words, and when I get home, there's not always a lot of that left.
Luckily for me, I've recently been able to go part-time and now have four-day weekends EVERY weekend, so I have more brain space for my fiction. Yay! And yet, if work is particularly demanding (like this week), it can take a couple of days for my brain to un-numb enough to make any real progress on the novel.
One strategy that's been helpful for me is not to work on my fiction at a computer. After spending all day wriitng at a computer, it's hard to go home and spend more time writing at a a computer. I used to write long-hand, but now I use an AlphaSmart. That way, I can carry the device anywhere I want to (a park, a pub, the sofa, the garden, my bed) and still write without feeling like I'm physically doing the same thing I did all day.