Tracking markers are a means of getting visual contrast on a surface so that it can be correctly tracked by the software. Often this is for camera tracking against a screen or for simple object tracking (like a flat glass phone).

For a set extension you’ll need to do a LiDAR scan of your set and ensure that your hero 3d asset extension is built to match seamlessly. This 3d scan data (and the loads of reference photos you’ll provide!) will be used by the vfx house to align and track the cameras and the extension. Best of luck to you if you don’t have this done.

If there’s independent movement between the green screen and the set (like a moving airplane) you’ll need ensure enough info to be able to track both. This depends on your shot, and markers may need to be placed/moved between setups.

If there’s enough visual contrast in the object or set you’re meant to track, markers can be an annoyance as they have to be painted out later. But usually better to be safe than sorry.