When you’ve got the enormous traffic necessary to work out if miniscule changes have some minor, statistically significant effect, then sure, if you can do it quickly, why wouldn’t you? But that’s optimization that should happen at the very end of the design cycle. The cart goes after the horse. Put it the other way ‘round and you have a broken setup. It doesn’t mean horses suck. It doesn’t mean carts suck. Carts are not the enemy of horses. Optimization is not the enemy of design. Get them in the right order and you have something really useful. Get them the wrong way around and you have something broken. - Nat Torkington