> No, you normally want that program to execute efficiently enough to do its required job

but... the "required job" is to go as fast as possible - in two ways :

1/ You must go faster than your competitors. Else people will switch, your software will get bad reviews, etc.

2/ you must go fast enough for anything that people will throw at you. And, in many cases, people can throw arbitrarily large problems to your program, and telling them "sorry but it will take 1 hour to process your 2TB dataset" just won't cut it at all. And even when you manage to cut it, then people come at you like "now can this run on a raspberry pi?"

Take for instance image processing software, audio or multimedia software... they will never be fast enough, and there is always an use case where getting a 1% perf improvement will allow a project to make instead of break (especially when working with uncompromising artists).