Generally, performance is something you worry about when it becomes an issue. Otherwise you spend waaaay too much time on "performance" that have 0 benefit. Th

Generally, performance is something you worry about when it becomes an issue. Otherwise you spend waaaay too much time on "performance" that have 0 benefit. That said “Avoid multiple passes over the data when one would do", while true, often profound performance gains comes from insight into the domain, where the first pass is structuring it such that the subsequent queries and transformations are simple and quick.