When you’re flying along a flight plan using your autopilot with the nav source engaged, you may think the heading bug is insignificant since it is not in use by the autopilot. But while the heading bug may not be active, it is worth keeping it centered as you fly along.
With the heading bug centered the display looks more streamlined. Unless you expect to turn to a specific heading, it simply makes more sense to have the heading bug on the current heading. And this way, once you engage heading mode on the autopilot, the airplane won’t turn in some random direction. Instead, the airplane stays stable until you turn the bug to the desired heading.
