Lead flashing, caulking, pipe, shower and tub liners, etc. As a test, I also had a test run on 'pure' lead from a chemical supply house. The dead-soft lead used for pipes, caulking, etc, that is so nice and soft when found in the junk yard was extruded, not cast. One source said tin and antimony were controlled to give more desired characteristics in the extrusion process. It pays to be aware of this when scrounging for lead.
Cost is a major factor.
The lead from the plumber was around a buck a pound. There is no safe way that a person at home can remove tin, antimony, etc from lead. Once it is alloyed, it requires a refinery to remove. Put your lead in the pot and start the heat. Once the lead is molten, you will need to flux.