I built a planked model designed by Henry Struck in 1940, so it's an old technique. So is balsa shell construction; there were some glider designs from the '30s made from two hollowed out halves.

With a decent hand plane that is set up properly you can shape a balsa turtle deck very quickly, much faster than you could glue planking over formers. There are no glue joints so it's probably lighter and you can get straighter, smoother contours. I guess those three things made block fuselages popular. It works for me, anyway.