A niche that is too narrow kills automated channels through content exhaustion. A channel posting daily on "horror stories about hotel rooms" will run out of distinct story angles within weeks. A channel posting on "horror stories" has unlimited content depth because the genre is infinitely extensible.
Finding the Right Breadth
The ideal niche is broad enough to generate 500+ unique stories but specific enough to have a clear audience identity. "Horror stories" is good. "Stories" is too broad -- the audience is unclear. "Workplace horror stories" is slightly too narrow for long-term sustainability. "Horror and thriller stories" is the sweet spot: broad enough for unlimited content, specific enough for a defined audience.