I learned this lesson through one of my optimization tasks. Speeding up programm by just reducing input data by 80% solved multiple problems. And real eye openner was an “article” about grep: https://lists.freebsd.org/pipermail/freebsd-current/2010-August/019310.html

Basically if you have less work you will do it faster. Since then my first question is always: Can we do less work?