Performance observation surfaced by Stephen Margheim: ActionView itself is very fast, but calling out to a partial is much slower because Rails must find and compile the partial file. Most applications accumulate 3–6 layers of partials (view → header partial → left/right partials → button partial). In Margheim's benchmarks, introducing just one partial (extracting a table row from an index view) made the endpoint 40% slower. SQLite was faster than ActionView in the same benchmarks, so partial depth often outweighs query cost. Lesson: fix slow queries but don't ignore partial depth.