alt Hacker NewsGreat question, I could answer with many stories but here are two:
The (deliberately) very limited analytics software I wrote for my personal website[0] could have used database but I didn't want to add a dependency to what was a very simple project so I hacked up an in-memory datastructure that periodically dumps itself to disk as a json file. This gives persistence across reboots and at a pinch I can just edit the file with a text editor.
Game design is filled with "stupid" ideas that work well. I wrote a text-based game[1] that includes Trek-style starship combat. I played around with a bunch of different ideas for enemy AI before just reverting to a simple action drawn off the top of a small deck. It's a very easy system to balance and expand, and just as fun for the player.