Its imperative every car owner gets the brake pads inspected for wear and be correctly advised to replace as neccessary at every periodic maintenance service. Its all documented in the car manual, but as a general guide. Nothing beats a competent inspection to determine brake wear, tear or defect. The harder you drive the car, the sooner a physical inspection needs to be done, no 2 ways about it. If you value your life, the car and unneccessary expense, go by the book, not by hearsay.