That's a good question, Prashun...the fact of the matter is that the wide belt sander is more efficient at final leveling. Yes, one can get a nice surface using the ROS with coarse through fine abrasives, but it's not going to be as flat as coming off the wide belt. The other thing here is that there is still a minor dip in the surface near the knots. These passes through the sander will absolutely take care of that. Using a ROS would mean there would still be a minor dip, although it would be smooth. That kind of thing is absolutely going to be visible once a finish goes on. The sander that BCH has (a really old-iron monstrosity) doesn't leave much marking, honestly. They process slabs on it daily for their own creations and then finish sand with Festool ROS just like I would.