I have to agree with husker in one point. Take a bank at the end of the year, 24 hours are short if you have some long running batch jobs, which take some hours. They have to be finished, before the regular jobs will start again. A million times tenth of a second is a difference. And - after all - CPU time costs on a mainframe.

But as I said another time in Structure is more important than speed, that's just a small part of the development business. Most times it is not worth to spend a single minute for micro-optimization.

And even for a bank it is more important, to have correct and not fast values in the end. They do not like optimized code, where nobody can fix that special case, that occured for the first time.

And it came to pass that in time the Great God Om spake unto Brutha, the Chosen One: "Psst!"
(Terry Pratchett, Small Gods)