“Do you by any chance know what else that early peoples used rendered fats for?”
We do not do “rendering” on the fats we use for making our soap. We might strain it. We have “rendered” beefalo fat trimmings in the oven, and used that for soap making. This was after having a beefalo butchered.
Fat such as the beefalo fat has been rendered in boiling water to make fat for deep frying. It is much healthier than any of the vegetable oils. We use coconut oil for this, because it is the healthiest oil to use for cooking. This, along with other fat from cooking goes into our soap.
Even rancid grease can be used for making soap. It does not adversely affect the quality of the soap.
Rendered fat (tallow) is also used in making candles. I have not tried that, but I am sure you can find info via Google search. You might also search for other uses for rendered animal fat or tallow.
The word tallow refers to fat rendered from BEEF, and the word lard refers to fat rendered from PORK. I’ll have to do some research on the tallow candles.