It's not always the sin it's made out to be. It's a matter of risk and cost. If there's a high risk performance will be an issue, and optimising later will have

It's not always the sin it's made out to be. It's a matter of risk and cost. If there's a high risk performance will be an issue, and optimising later will have a high cost (or optimising early has a low cost), then it makes sense.