I don't sand much with it (fairing board) as a ROS does just fine.
Randy

If your boat forms are set properly and your strips stay in contact with the forms your hull surface will start off fair.

Irregular surfaces are created by haphazard sanding technique.

Big powerful sanders, with the wrong grit sandpaper, naturally incline the user to apply heavy pressure in linear strokes destroying the fair surface requiring a fairing board to rectify.

Professional shops don't teach workers to sand and sanding is often the job given to the new and least experienced worker. So fairing boards are a routine follow-up.

If you've used a ROS for any period of time you learn if you start the sander before contact with the wood, the high speed spinning disk touches the surface and cuts very aggressively. This is the key to using the ROS.

By holding the ROS lightly against the wood, even lifting it off the surface occasionally, the disk speed will remain high and it will cut most aggressively. The combination of holding the ROS lightly and sanding in small circles will allow the sander to follow the fair hull surface keeping it fair.

A smaller more lightweight ROS is better for doing this than a heavier more powerful ROS which will be harder to handle and follow the surface curves.

For more details on learning to sand quickly and keep the hull fair see - http://www.laughingloon.com/sanding.html