I have made liquid soap only once and do add Germall Plus to it after reconstituting the paste with water. I only use it for shaving my legs and underarms, so it lasts a long time and I certainly don't want to introduce any unwanted microbes to the potentially tender areas, especially since I cannot know for sure I might not nick myself shaving. At first I didn't care, but when I gave some to my granddaughter, it became important to me to add the Germall Plus.
I would recommend it in body scrubs, too because people, me included, tend to use them while in the shower or tub and dip wet hands into the container to pull out the scrub. This introduces water and subsequently the potential for microbial contamination.
I've never made lotions or creams, but depending on the recipe, I would consider it there as well.
For obvious reasons, I do not use any preservatives in bar soap.
Germall Plus is the only one I have used, so I cannot address the question regarding Natural antimicrobial preservatives. Someone else will surely come along with more information.