In The Practice of Programming Kernighan and Pike say that one should estimate how much time can be saved over the expected runs of the program and allocate no

In The Practice of Programming Kernighan and Pike say that one should estimate how much time can be saved over the expected runs of the program and allocate no more than that much time to optimization. If you're doing something once or once per year that takes 45 seconds rather than 30 then don't bother. If you're doing it once every hour, that's six minutes a day, 365 days a year. If it's on a minutely cron on a hundred systems, that's 144,000 seconds a day. If a few hours of time can save you 144,000 seconds of runtime every day, that's a clear winner assuming other higher priority things are done. If it's run minutely by thousands of customers on hundreds of thousands of servers...