Doing water changes replenishes the used trace elements needed for your corals to grow. Most people don't have the means to test/dose all the replaced nutrients that a 10-20% PWC
will do. Water changes are a great time to remove detrius and leftover food.
Water changes are more beneficial than what is measured in these test kits.
Are they required? Not entirely, I've read about tanks in other forums reaching 40 years old with 5 water changes a year, but I would never reccommend that to anyone.
Also, yes 10% water changes per week is great. Use that water change wisely and remove what detrius you can.