> (though the resistor bit I'm not sure on why they don't just buy high precision ones for a few cents more) high precision resistors can get expensive, aren't

> (though the resistor bit I'm not sure on why they don't just buy high precision ones for a few cents more) high precision resistors can get expensive, aren't always readily available (depending on your volume), or simply might not be available in the power rating you need. especially if you don't need absolute precision you might consider it wasteful. so it's good to know how to match resistors when you're designing/prototyping the circuit. because of that, it's probably become hearsay and superstition, and is consequently overused.