The one feature I almost cut from my MVP saved the product

When I was building Reoogle, I was obsessed with keeping the MVP lean. The core was the database of subreddits with inactive mods. The 'Best Posting Time Analyzer' was an afterthought—a nice-to-have I almost left for a later version. I threw it in at the last minute. Fast forward a few months, and that feature is the primary reason users cite for sticking around. It turned a niche research tool into a practical daily planner for Reddit engagement. The tool is at https://reoogle.com. It taught me that sometimes the feature you consider secondary solves the most immediate, tangible pain point for your user. Has anyone else had a similar experience where an 'extra' feature became the main attraction?