I suppose if you're doing one you're not doing the other - the promise of future horizontal scale definitely justifies a lot of arguments about premature optimi

I suppose if you're doing one you're not doing the other - the promise of future horizontal scale definitely justifies a lot of arguments about premature optimization. However, they aren't necessarily opposed. Optimization is usually subtractive - it's slicing parts off the total runtime. Horizontal scale is multiplicative - you're doing the same thing more times. Outside some very specific limits, usually efficiency means horizontal scaling is more effective. A slightly shorter runtime many times over means a much shorter runtime.