Lost art of using Lead and not bondo

Earlier today I jumped at the chance to be taught a few welding and metal work things from a local ford guy. Great guy, does fantastic work. Before I left I had a enough knowledge and skill from him walking me step by step on how to replace a floor pan on an old falcon. I did the labor, he supervised and made sure I did it a correct way that was as good as the factory. When I went to leave, he asked me if I knew anything about using lead and pointed at the roof line on my Valiant. The three lines in the roof at the rear pillars. He said come on back when you want to learn an art that is being lost. Long story short, I actually have lead, a torch, and the files and metal scrape needed. Turns out my grandfather was one of those guys. I always wondered what those rods were, now I know. So glad I didn't throw them away. Is this something that is still used today on old cars? Or is everyone moving to bondo? Or kitty hair and fiberglass? Given the chance, would this be something worth learning?