I put walks into a category of activities like strength work and yoga - likely good for my running, but not quantifiable in an apples-to-apples way to actual running. I just create a separate category for those things in my log.
Walking is good for recovery, not much else. So in my opinion the only reason to log walks in your training log is to get a better sense of what works for you overall. When you look at it in the future, you might see patterns that aren't visible in real-time, like that you seemed to hit your next workout harder if you incorporated walking into your routing.
But if you're like me and you want "credit" for walking in your running training log, you are SOL.