Lead? I don't know how lead got into the discussion. At the solder factory, I was working with alloys of copper, tin, antimony, and silver. We made filler metals for solder, brazing, and welding. While the alloys I made were different than brass (no zinc) the general methods and reasons for annealing were the same. If you wanted to make something more brittle, you beat on it or heated it and let it cool slowly. If you wanted to make something more pliable, you heated it just enough and quenched it quickly.
General reasons for annealing - yes, but the methods you describe apply to the alloys you were working with, not cartridge brass. You cannot make cartridge brass harder or brittle by heating and cooling slowly - it doesn't work that way. Different metal types have different requirements for annealing; you really can't assume that something like solder reacts the same way as cartridge brass.
Also, it's important to recognize that when we talk about "annealing" cartridge brass, we're not fully annealing it, we're only drawing back the hardness to a certain point - we're really tempering the brass rather than annealing. When we hear of brass that's "ruined" from getting too hot, usually it just means that brass was fully annealed (unless the heat was really excessive), making it too soft for our reloading needs.
