I learned the power of small, frequent optimizations at my first job many moons ago. One of the guys sitting next to me was messing around with the custom string class this company made (this was an old, old, old C/C++ product), and for our use case, it turned out that a small 1 line tweak to our string compare was an 80-90% speed improvement or something equally crazy.
And given the speed of computers, AND how frequently huge strings were compared, this actually was a genuine perf improvement that could be felt in some parts of the app