Or it only accepts certain inputs, or has an expensive first invocation but amortized cost, or is not bug-compatible with the old `convert`, or it requires a la

Or it only accepts certain inputs, or has an expensive first invocation but amortized cost, or is not bug-compatible with the old `convert`, or it requires a large cache, or it's optimized for parallelism, or uses instructions only available in newer CPUs, or it was a prototype that stuck around, or...