As to caring about perf, you shouldn't care about it until you have to. Take that 2h vs 20min example, for instance. If you only need to run it a few times and there's plenty of time available, who cares how long it takes. If the 2h one is easier to write that's by all means what you should do. OTOH if you're under severe time constraints and need to run it every hour, then obviously 2h script won't do the job. Or alternatively if 20 min script takes the same time to write as 2h one, then of course you should go with it. All too often I see people optimizing things that don't matter one iota, simply because they like things to be fast. Something gets executed once a day and runs for 5 minutes? Let's spend two weeks making it complete in 30 seconds. As long as the employer is paying, why not.
