Many of the routes I drive are extremely familiar to me. So, I know when to turn and where. I will ignore Waze if I know a better route that the one recommended. However, it's possible that Waze knows about traffic or other issues ahead, and is sending me an otherwise suboptimal or longer route for that reason. There should be a verbal and visual announcement built into the interface that tells me something like, "Waze is directing you around traffic ahead," or "Construction ahead, Waze is re-routing you," etc. Because Waze makes mistakes still, I can't trust directions that seem illogical. However, if I knew it knew that there is normally a faster way, then I'd be able to make better decisions as to whether to follow the seemingly less direct path.
I find this hard to describe, so maybe this real scenario would help: I approach an intersection on my beach drive. Waze says go straight. All the signs, my older TomTom GPS, and my 20 years experience, say go left. The time shown on Waze to the destination is way longer than my normal route would take under normal conditions. I ignore Waze, and turn left. Waze attempts to U-turn me numerous times. I'm thinking, "I wonder if there is a issue ahead. Maybe I should turn around and go the other route, even if it says it will take 40 minutes more than I'm used to, because there's a huge construction zone or accident ahead. Why does it want me to go that way. It doesn't make sense."
In the above scenario, Waze was wrong. At some point, it stopped trying to get me to do a U-turn, and the time to destination plummeted to well below it's pre-turn estimate. But, again, I just don't have a visual indicator as to why Waze is picking a particular route. Is it the standard route, if there were no "issues" ahead, or is it some sort of a D-tour around an "issue".
Hope this helps. I think it would be hugely useful!