A couple of definitions:

• Acting or producing effectively with a minimum of waste, expense, or unnecessary effort.
• Exhibiting a high ratio of output to input.

Moore’s law defence:

• Computers double in speed every 18 months. Why bother re-working your code when you can just wait 18 months and get a faster machine?

Overly-simplistic example:

• Let’s say we have a movie player which runs at 10fps. Our competitor has a movie player which runs at 20fps.
• If we don’t optimise our player, in 18 months’ time our competitor’s player will be running at 40fps. We’ll be running at 20fps. Only half as fast.
• If we beat them now, we’ll be able to beat them in future.

Future-proofing:

• In 18 months’ time we’ll be on version N + 1 of the software. Which will have even more features to support.