I had a product to help political campaigns canvas neighborhoods door to door. In the early days there was a "smart walk sheet" feature, which would magically pick the optimal doors to knock given how much time you had (e.g. 2 hours after work).

While I was building out this feature, I'd stay up late in the night manually selecting clusters of houses and setting them for the customer, so the next morning they'd be greeted with what looked like our backend systems auto-magically picking the perfect cluster of houses.

The bonus of doing it manually for a while is that I found a lot of edge cases I would have missed otherwise. The initial release of the finished feature was rock solid thanks to what I learned.