Just on sheeted areas. If you use water base polyurethane (WBPU), you should first apply a couple of coats to the bare wood first. Otherwise the balsa absorbs the WBPU very quickly. Using WBPU is quick and easy, no smell and water clean up. Here's a pic of the nose of my restored Perigee, 3/4 oz cloth and WBPU. It went around the curves like they weren't there.

FB