Most of the shops I do require detailed narratives, and I spend a long time doing them. That's why I usually won't do a shop without a bonus, and why I don't do as many shops as most other people here. But, as a copywriter by trade, I enjoy the writing.
In my narratives, I basically just "tell the story" of my visit, making sure that I include mention of every area covered by the survey, even though I've already addressed them in my short-form answers. When I "think" I'm finished, I verify that my narrative comments agree with my responses and that I've covered all areas.
It's frustrating when the narrative boxes allow for a limited number of characters, and that's not stated anywhere! I once spent 15 minutes trying to edit down an answer that made sense and fit into the limit. Too much time. I won't do that particular shop ever again (not just for that reason, but the whole thing is way too time intensive for the pay--and it was bonused to boot!).
I've been told that the end clients want to read your narrative and feel as if they were there with you. So, that's what I give 'em!
I learn something new every day, but not everyday!
I've learned to never trust spell-check or my phone's auto-fill feature.