It depends. You must do whatever is necessary to avoid gaps or thick glue lines in your turning. Even if you get the angle correct off the saw but have imperfections on the surface of the segment edge, you will see a gap. If you have a saw with no blade wobble and have a sharp blade, sanding may not be needed. Look at each surface before gluing and check for kerf marks or other imperfections. Sand if you need too.
