It’s wasteful of other peoples time to show up to a meeting late, and wasteful of my own to be early. I’d like to be as precise as practical. Meetings filled with high paid experts are incredibly expensive- one should get every detail right to save time. One little thing might not matter, but if you pay attention to a lot of little details in running a meeting efficiently- including starting as close to on time as you can, it saves a lot of time.